Zix (ZIXI) 10-K 5 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 03, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	ZIXI
Entity Registrant Name	ZIX CORP
Entity Central Index Key	0000855612
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Entity File Number	0-17995
Entity Tax Identification Number	75-2216818
Entity Address, Address Line One	2711 N. Haskell Avenue
Entity Address, Address Line Two	Suite 2300, LB 36
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75204-2960
City Area Code	214
Local Phone Number	370-2000
Title of 12(b) Security	Common Stock$0.01 Par Value
Entity Incorporation, State or Country Code	TX
Entity Filer Category	Accelerated Filer
Document Annual Report	true
Document Transition Report	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		57,090,291
Entity Public Float			$ 386,416,684
Documents Incorporated by Reference	Portions of the Registrant’s 2021 Proxy Statement are incorporated by reference into Part III of this Form 10-K.
ICFR Auditor Attestation Flag	true

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 21,362	$ 13,349
Receivables, net	16,831	10,081
Prepaid and other current assets	5,430	4,984
Total current assets	43,623	28,414
Property and equipment, net	7,345	8,591
Operating lease assets	14,259	10,128
Intangible assets, net	144,163	145,876
Goodwill	195,013	171,209
Deferred tax assets	32,554	36,535
Deferred costs and other assets	12,767	11,968
Total assets	449,724	412,721
Current liabilities:
Accounts payable	20,018	14,400
Accrued expenses	10,364	13,732
Deferred revenue	40,447	40,757
Current portion of long-term debt	2,205	1,850
Operating lease liabilities, current	5,156	2,947
Finance lease liabilities, current	602	1,338
Total current liabilities	78,792	75,024
Long-term liabilities:
Deferred revenue	1,079	2,524
Noncurrent operating lease liabilities	10,094	8,389
Noncurrent finance lease liabilities	114	716
Long-term debt, net of issuance costs	209,658	178,250
Total long-term liabilities	220,945	189,879
Total liabilities	299,737	264,903
Commitments and contingencies (Note 17)
Preferred stock:
Convertible preferred stock	115,552	106,527
Stockholders’ equity:
Preferred stock, $1 par value, 10,000,000 shares authorized; none issued and outstanding
Common stock, $0.01 par value, 175,000,000 shares authorized; 85,382,484 issued and 57,246,521 outstanding in 2020 and 83,393,514 issued and 55,640,397 outstanding in 2019	782	780
Additional paid-in capital	401,646	391,605
Treasury stock, at cost; 28,135,963 common shares in 2020 and 27,753,117 common shares in 2019	(113,031)	(110,298)
Accumulated deficit	(256,548)	(240,995)
Accumulated other comprehensive income, net of tax	1,586	199
Total stockholders’ equity	34,435	41,291
Total liabilities, preferred stock and stockholders’ equity	449,724	412,721
Series A Convertible Preferred Stock [Member]
Preferred stock:
Convertible preferred stock	$ 115,552	$ 106,527

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	85,382,484	83,393,514
Common stock, shares outstanding	57,246,521	55,640,397
Treasury stock, shares	28,135,963	27,753,117
Series A Convertible Preferred Stock [Member]
Convertible Preferred stock, par value	$ 1	$ 1
Convertible Preferred stock, shares designated	100,206	100,206
Convertible Preferred stock, shares issued	100,206	100,206
Convertible Preferred stock, shares outstanding	100,206	100,206

Consolidated Statements of Comp

Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues	$ 218,478	$ 173,428	$ 70,478
Cost of revenue	112,763	76,908	15,186
Gross margin	105,715	96,520	55,292
Operating expenses:
Research and development expenses	22,813	20,431	11,323
Selling, general and administrative expenses	78,345	85,230	33,999
Operating income (loss)	4,557	(9,141)	9,970
Other (expense) income:
Investment and other income (expense)	83	121	754
Interest (expense)	(9,325)	(10,105)
Total other (expense) income	(9,242)	(9,984)	754
(Loss) Income before income taxes	(4,685)	(19,125)	10,724
Income tax (expense) benefit	(1,740)	4,478	4,720
Net (loss) income	(6,425)	(14,647)	15,444
Deemed and accrued dividends on preferred stock	9,025	9,984
Net (loss) income attributable to common stockholders	$ (15,450)	$ (24,631)	$ 15,444
Basic (loss) income per share attributable to common stockholders	$ (0.29)	$ (0.46)	$ 0.29
Diluted (loss) income per common share attributable to common stockholders	$ (0.29)	$ (0.46)	$ 0.29
Basic weighted average common shares outstanding	54,024,162	53,025,152	52,591,714
Diluted weighted average common shares outstanding	54,024,162	53,025,152	53,481,295
Other comprehensive (loss) income, net of tax:
Foreign currency translation adjustments	$ 1,387	$ 215	$ (16)
Comprehensive (loss) income	$ (5,038)	$ (14,432)	$ 15,428

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($)	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]Series A Convertible Preferred Stock [Member]	Preferred Stock [Member]Series B Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Deficit [Member]Series A Convertible Preferred Stock [Member]	Accumulated Deficit [Member]Series B Convertible Preferred Stock [Member]	Accumulated Other Comprehensive Income (Loss), net of tax [Member]
Beginning balances at Dec. 31, 2017	$ 43,520,000							$ 778,000	$ 381,457,000	$ (102,343,000)	$ (236,372,000)
Beginning balance, shares at Dec. 31, 2017								80,709,970
Cumulative effect adjustment from changes in accounting standards (Note 2) at Dec. 31, 2017		$ 4,564,000										$ 4,564,000
Beginning balances, as adjusted at Dec. 31, 2017	48,084,000							$ 778,000	381,457,000	(102,343,000)	(231,808,000)
Issuance of common stock upon exercise of stock options	$ 166,000							$ 1,000	165,000
Issuance of common stock upon exercise of stock options, shares	90,011							90,011
Issuance of common stock upon vesting of restricted stock units, net, shares								50,751
Issuance of common stock upon vesting of performance stock units, net, shares								32,665
Issuance of restricted common stock, net, shares								735,987
Issuance of restricted performance common stock, net, shares								95,946
Employee stock-based compensation costs	$ 2,662,000								3,318,000	(656,000)
Treasury repurchase program	(5,393,000)									(5,393,000)
Adjustment from foreign currency translation	(16,000)														$ (16,000)
Net income (loss)	15,444,000										15,444,000
Ending balance at Dec. 31, 2018	60,947,000							$ 779,000	384,940,000	(108,392,000)	(216,364,000)				(16,000)
Ending balance, shares at Dec. 31, 2018								81,715,330
Issuance of preferred stock in connection with private placement						$ 62,662,000	$ 33,881,000
Issuance of preferred stock in connection with private placement, shares						64,914	35,086
Issuance of Series A preferred stock for dividend on Series B preferred stock upon conversion to Series A preferred, shares					206
Beneficial conversion feature of preferred stock			$ (1,407,000)	$ (1,067,000)		$ 1,407,000	$ 1,067,000						$ (1,407,000)	$ (1,067,000)
Accretion of beneficial conversion feature of Preferred Shares (Participating)			(99,000)	(35,000)		99,000	35,000						(99,000)	(35,000)
Accrued dividend on preferred stock			$ (6,159,000)	(1,030,000)		6,159,000	1,030,000						(6,159,000)	(1,030,000)
Redemption accretion of preferred stock				(187,000)			187,000							(187,000)
Issuance of common stock upon exercise of stock options	$ 415,000							$ 1,000	414,000
Issuance of common stock upon exercise of stock options, shares	167,438							167,438
Issuance of common stock upon vesting of restricted stock units, net, shares								43,667
Issuance of common stock upon vesting of performance stock units, net, shares								7,000
Issuance of restricted common stock, net, shares								1,117,579
Issuance of restricted performance common stock, net, shares								342,500
Employee stock-based compensation costs	$ 4,345,000								6,251,000	(1,906,000)
Adjustment from foreign currency translation	215,000														215,000
Net income (loss)	(14,647,000)										(14,647,000)
Ending balance at Dec. 31, 2019	41,291,000							$ 780,000	391,605,000	(110,298,000)	(240,995,000)				199,000
Ending balance, shares at Dec. 31, 2019			100,206		100,206
Ending balances at Dec. 31, 2019	106,527,000		$ 106,527,000		$ 106,527,000
Ending balance, shares at Dec. 31, 2019								83,393,514
Cumulative effect adjustment from changes in accounting standard (Note 2) at Dec. 31, 2019		$ (103,000)										$ (103,000)
Ending balances, as adjusted at Dec. 31, 2019	41,188,000				$ 106,527,000			$ 780,000	391,605,000	(110,298,000)	(241,098,000)				199,000
Accretion of beneficial conversion feature of Preferred Shares (Participating)			(125,000)	(67,000)		125,000	67,000						(125,000)	(67,000)
Accrued dividend on preferred stock			$ (5,754,000)	$ (3,079,000)		$ 5,754,000	$ 3,079,000						$ (5,754,000)	$ (3,079,000)
Issuance of common stock upon exercise of stock options	$ 334,000							$ 2,000	332,000
Issuance of common stock upon exercise of stock options, shares	114,375							114,375
Issuance of common stock upon vesting of restricted stock units, net, shares								112,799
Issuance of common stock upon vesting of performance stock units, net, shares								48,910
Issuance of restricted common stock, net, shares								1,334,806
Issuance of restricted performance common stock, net, shares								378,080
Employee stock-based compensation costs	$ 6,976,000								9,709,000	(2,733,000)
Adjustment from foreign currency translation	1,387,000														1,387,000
Net income (loss)	(6,425,000)										(6,425,000)
Ending balance at Dec. 31, 2020	34,435,000							$ 782,000	$ 401,646,000	$ (113,031,000)	$ (256,548,000)				$ 1,586,000
Ending balance, shares at Dec. 31, 2020			100,206		100,206
Ending balances at Dec. 31, 2020	$ 115,552,000		$ 115,552,000		$ 115,552,000
Ending balance, shares at Dec. 31, 2020								85,382,484

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	Feb. 20, 2019	Dec. 31, 2020
Series A Convertible Preferred Stock [Member]
Preferred stock, net of issuance costs	$ 2,300	$ 2,253
Series B Convertible Preferred Stock [Member]
Preferred stock, net of issuance costs	$ 1,200	$ 1,204

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net (loss) income	$ (6,425)	$ (14,647)	$ 15,444
Non-cash items in net (loss) income:
Depreciation and amortization	32,329	24,429	3,706
Amortization of debt issuance costs	1,355	967
Employee stock-based compensation expense	9,710	6,251	3,318
Noncash lease costs	3,279	2,828
Changes in deferred taxes	2,335	(4,296)	(4,754)
Changes in operating assets and liabilities:
Receivables	(5,935)	(369)	(1,376)
Prepaid and other assets	(234)	(1,036)	108
Deferred costs and other assets	(943)	(2,347)	(3,139)
Accounts payable	5,521	6,121	(325)
Deferred revenue	(3,112)	(1,356)	1,892
Payment of acquisition related contingent consideration		(582)	(195)
Accrued and other liabilities	(6,600)	(2,012)	1,992
Net cash provided by operating activities	31,280	13,951	16,671
Investing activities:
Purchases of property, equipment and internal-use software	(18,010)	(11,653)	(4,179)
Acquisition of business, net of cash acquired	(30,046)	(284,590)	(11,773)
Net cash used in investing activities	(48,056)	(296,243)	(15,952)
Financing activities:
Proceeds of long-term debt	41,000	187,000
Debt issuance cost	(653)	(6,444)
Deferred debt financing costs			(60)
Repayment of long-term debt	(9,939)	(1,363)
Proceeds from issuance of preferred stock, net of offering costs		96,588
Payment of acquisition related contingent consideration	(1,125)	(3,843)	(605)
Proceeds from exercise of stock options	334	415	166
Stock issuance costs			(45)
Purchase of treasury stock	(2,733)	(1,906)	(6,049)
Repayment of finance lease liabilities	(1,339)	(1,707)
Net cash provided by (used in) financing activities	25,545	268,740	(6,593)
Effect of exchange rate changes on cash	(756)	(208)	(26)
Increase (decrease) in cash and cash equivalents	8,013	(13,760)	(5,900)
Cash and cash equivalents, beginning of year	13,349	27,109	33,009
Cash and cash equivalents, end of year	$ 21,362	$ 13,349	$ 27,109

Company Overview

Company Overview	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Company Overview	1. Company Overview Zix Corporation (“Zix,” the “Company,” “we,” “our,” “us”) is a leading cloud provider of email security, compliance and productivity solutions, with easy-to-use solutions for email encryption, data loss prevention (“DLP”), advanced email threat protection, unified archiving, and cloud data backup to meet the data protection and compliance needs of our customers in a variety of industries.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation — The accompanying consolidated financial statements include the accounts of all our wholly-owned subsidiaries and are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All inter-company accounts and transactions have been eliminated in consolidation. Use of Estimates — The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reported period. Our significant estimates include primarily those required in the valuation or impairment analysis of goodwill and intangibles, property and equipment, revenue recognition, amortization period of our commission amortization, allowances for doubtful accounts, stock-based compensation, litigation accruals, valuation allowances for deferred tax assets and tax accruals. Although we believe that adequate accruals have been made for unsettled issues, additional gains or losses could occur in future years from resolutions of outstanding matters. These estimates and assumptions take into account historical and forward-looking factors that the Company believes are reasonable, including, but not limited to the potential impacts arising from the recent coronavirus (COVID-19) and public and private sector policies and initiatives aimed at reducing its transmission. As the extent and impacts of the COVID-19 virus remain unclear, the Company’s estimates and assumptions may evolve as conditions change. Actual results could differ materially from original estimates. Cash Equivalents — Cash investments with maturities of three months or less when purchased are considered cash equivalents Fair Value of Financial Instruments —The Company does not measure the fair value of any financial instrument other than cash equivalents, options, and other equity awards. The carrying values of other financial instruments (receivables and accounts payable) are not recorded at fair value but approximate fair values primarily due to their short-term nature. The carrying values of other current assets and accrued expenses are also not recorded at fair value, but approximate fair values primarily due to their short-term nature. In addition, the Company measures its long-term debt at fair value which approximates book value as the long-term debt bears market rate. Valuation of Property and Equipment — The accounting policies and estimates relating to property and equipment are considered significant because of the potential impact that impairment, obsolescence, or change in an asset’s useful life could have on the Company’s operating results. We record an impairment charge on the assets to be held and used when we determine based upon certain triggering events that the carrying value of property and equipment may not be recoverable based on expected undiscounted cash flows attributable to such assets. The amount of a potential impairment is determined by comparing the carrying amount of the asset to either the value determined from a projected discounted cash flow method, using a discount rate that is considered to be commensurate with the risk inherent in the Company’s current business model or the estimated fair market value. Assumptions are made with respect to future net cash flows expected to be generated by the related asset. An impairment charge would be recorded for an amount by which the carrying value of the asset exceeded the discounted projected net cash flows or estimated fair market value. Also, even where a current impairment charge is not necessary, the remaining useful lives are evaluated. No impairment was recorded for any of the periods presented. Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over their estimated useful lives as follows: computer and office equipment and software — three years; leasehold improvements — the shorter of five years or the lease term; and furniture and fixtures — five years. We recorded depreciation expense of $5.0 million for the year ended December 31, 2020. We allocated $4.4 million of the expense to cost of revenue, $377 thousand to research and development expense, and $253 thousand to selling, marketing, and general and administrative expenses. Goodwill and Other Intangible Assets — We account for the valuation of goodwill and other intangible assets after classifying intangible assets into three categories: (1) intangible assets with finite lives subject to amortization; (2) intangible assets with indefinite lives not subject to amortization; and (3) goodwill. For intangible assets with finite lives, tests for impairment must be performed if conditions exist that indicate the carrying value may not be recoverable. For intangible assets with indefinite lives and goodwill, tests for impairment must be performed at least annually or more frequently if events or circumstances indicate that assets might be impaired. Goodwill was $195.0 million, or 43%, and $171.2 million, or 41%, of total assets as of December 31, 2020 and 2019, respectively. We evaluate the goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. Evaluations for possible impairment are based upon a comparison of the estimated fair value of the reporting unit to which the goodwill has been assigned, versus the sum of the carrying value of the assets and liabilities of that unit including the assigned goodwill value. We include our entire Company as the reporting unit. The fair values used in this evaluation are estimated based on the Company’s market capitalization, which is based on the outstanding stock and market price of the stock. Impairment is deemed to exist if the net book value of the unit exceeds its estimated fair value. No impairment was recorded for any of the periods presented. Our intangible assets with finite lives are amortized using a straight line basis over their economic useful lives. Deferred Tax Assets — Deferred tax assets are recognized if it is “more likely than not” that the benefit of our deferred tax assets will be realized on future federal or state income tax returns. At December 31, 2020, we provided a valuation allowance against a significant portion, $25.2 million, of our accumulated deferred tax assets, reflecting our historical losses and the uncertainty of future taxable income sufficient to utilize net operating loss carryforwards prior to their expiration. Our total deferred tax assets not subject to a valuation allowance are valued at $32.6 million, and consist of $26.9 million of federal net operating loss carryforwards, $4.4 million relating to temporary timing differences between U.S. GAAP and tax-related expense, $1.9 million in federal R&D credits, and $1.0 million relating to U.S. state income tax and other credits. These items are offset by a $1.6 million deferred tax liability associated with our CloudAlly acquisition. If our U.S. taxable income increases from its current level in a future period or if the facts and circumstances on which our estimates and assumptions are based were to change, thereby impacting the likelihood of realizing our deferred tax assets, judgment would have to be applied in determining the amount of valuation allowance no longer required. Reversal of all or a part of this valuation allowance could have a significant positive impact on operating results in the period that it becomes more likely than not that certain of the Company’s deferred tax assets will be realized. Alternatively, should our future income decrease from current levels, a resulting increase to all or a part of this valuation allowance could have a significant negative impact on our operating results Uncertain Tax Positions — Our Company recognizes and measures uncertain tax positions using a two-step approach. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon settlement. Right-of-use Assets and Lease Obligations — On January 1, 2019, we adopted Accounting Standards Update No. 2016-02, Leases (Topic 842) (ASU 2016-02) using the modified retrospective transition approach by applying the new standard to all leases existing at the date of initial application. Results and disclosure requirements for reporting periods beginning after January 1, 2019, are presented under Topic 842, while prior period amounts have not been adjusted and continue to be reported in accordance with our historical accounting under Topic 840. We elected to combine our lease and non-lease components and to keep leases with an initial term of 12 months or less off the balance sheet and recognize the associated lease payments in the consolidated statements of comprehensive income (loss) on a straight-line basis over the lease term. Additionally, for certain equipment leases, we apply a portfolio approach to effectively account for the finance lease right-of-use (ROU) assets and lease liabilities. Under Topic 842, we determine if an arrangement is a lease at inception. ROU assets and lease liabilities are recognized at commencement date based on the present value of remaining lease payments over the lease term. For this purpose, we consider only payments that are fixed and determinable at the time of commencement. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. Our incremental borrowing rate is the financing rate of our long-term debt at the commencement date. The ROU asset also includes any lease payments made prior to commencement and is recorded net of any lease incentives received. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise such options. When determining the probability of exercising such options, we consider contract-based, asset-based, entity-based, and market-based factors. Our lease agreements may contain variable costs such as common area maintenance, insurance, real estate taxes or other costs. Variable lease costs are expensed as incurred on the consolidated statements of income. Our lease agreements generally do not contain any residual value guarantees or restrictive covenants. Operating leases and finance leases are included in operating lease assets and property and equipment, respectively, on the consolidated balance sheets. Operating lease and finance lease liabilities are separately presented on our consolidated balance sheets. Revenue Recognition — In May 2014, The Financial Accounting Standards Board (“FASB”) issued ASC 606 which requires revenue recognition when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled to those goods and services. The standard became effective for us in 2018 but did not have a material impact to our revenue recognition process. We earn our revenue from subscription fees for rights related to the use of our software. Approximately 78% of our revenue in 2020 was derived from hosted solutions. While some contracts include one or more performance obligations, the revenue recognition pattern generally is not impacted by separate allocations of these obligations because the services are generally satisfied over the same period of time and revenue is recognized ratably over the contract term. Our subscription terms historically have ranged from one to five years. We are increasingly moving to a monthly subscription model. This shift has been largely driven by our recent acquisition activity. As we further integrate our business, we expect to focus on a monthly subscription model. Revenue is recognized by applying the following steps: • Step 1: Identify the contract(s) with a customer, • Step 2: Identify the performance obligations in the contract, • Step 3: Determine the transaction price • Step 4: Allocate the transaction price to the performance obligations in the contract, and • Step 5: Recognize revenue when (or as) the performance obligation is satisfied. Step 1: Identify the contract(s) with a customer: We consider the terms and conditions of the contract and our customary business practice in identifying our contracts. We determine we have a contract with a customer when the contract is approved, we can identify each party’s rights regarding the services and products transferred, we can identify the payment terms for the services and products, the contract has commercial substance, and it is probable we will be paid. Step 2: Identify the performance obligations in the contract: ASC 606 requires identification and disclosure of performance obligations within a revenue contract. A good or service is considered distinct if the customer can both benefit from the good or service on its own or with other resources that are readily available to the customer, and the promise to transfer the good or service is separately identifiable from other promises in the contract. Step 3: Determine the transaction price: The transaction price is determined based on the consideration we expect to be entitled to receive in exchange for transferring goods and services to the customer. We include variable consideration in the transaction price if we view it as probable that a significant future reduction of cumulative revenue under the contract will not occur. Step 4: Allocate the transaction price to the performance obligations in the contract: We allocate transaction prices to each performance obligation based on the stand-alone selling price of our component services. Step 5: Recognize revenue when (or as) the performance obligation is satisfied: We begin recognize revenue when the customer obtains control of the product or services, at the amount allocated to the satisfied performance obligation. Our performance obligations are generally satisfied over time. While some contracts include one or more performance obligations (including the combined elements noted above along with additional ongoing customer support and other hosted services), the revenue recognition pattern generally is not impacted by the separate allocations of these obligations because the services are generally satisfied over the same period of time and revenue is recognized over the contract period. Discounts provided to customers are recorded as reductions in revenue. Commission Amortization — We amortize our commission costs to expense on a systemic basis over the period of expected benefit to the customer. Determination of the amortization period requires significant judgement. We apply the practical expedient noted in ASC 606-10-10-4 to account for our commission costs and related amortizations at the portfolio level. Additionally, the Company has evaluated commissions earned upon contract renewal as compared to initial commissions paid and determined that because commissions paid were not reasonably proportional to their respective contract values, our renewal commissions could not be considered commensurate with the initial commissions paid. We considered our average contract term length and historical customer retention rates to determine an average length of our customer relationships. We also concluded our add-on sales generally occur halfway into our customer relationships and evaluated our average customer renewal terms. Based on these factors we have determined that 8 years, 4 years and 18 months are the appropriate amortization periods to our new, add-on, and renewal sales commission expenses, respectively. We also perform subsequent assessments for impairment of the related deferred cost asset when indicators present. Following our acquisition of AppRiver in February 2019, we additionally evaluated AppRiver’s sales program to determine whether capitalization of these expenses was appropriate. While we determined certain costs to acquire customers met the capitalization criteria, we also determined renewal commissions earned were commensurate to the initial sales. Based on AppRiver’s primarily month-to-month commitments the Company has chosen to apply the practical expedient approach to immediately recognize such commensurate commission expenses associated with the AppRiver program. Internal Use Software — The Company capitalizes costs related to its cloud email security, productivity and compliance solutions and certain projects for internal use incurred during the application development stage. Costs related to preliminary project activities and post implementation activities are expensed as incurred. Internal-use software is amortized on a straight-line basis over its estimated useful life, which is generally three years. Management evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. In 2020, we capitalized $14.2 million of costs related to internal-use software. The Company expects our capitalization of these costs to increase in the future. Advertising Expense — Advertising costs are expensed as incurred. Our operations include advertising expense of $2.4 million, $4.3 million, and $1.1 million in 2020, 2019, and 2018, respectively Stock-Based Compensation — We currently use the straight-line amortization method for recognizing stock option and restricted stock compensation costs. The measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors are based on the estimated fair value of the awards on the grant dates. The grant date fair value is estimated using either an option-pricing model which is consistent with the terms of the award or a market observed price, if such a price exists. Such cost is recognized over the period during which an employee or director is required to provide service in exchange for the award, i.e., “the requisite service period” (which is usually the vesting period). We also estimate the number of instruments that will ultimately be earned, rather than accounting for forfeitures as they occur. Earnings Per Share (“EPS”) — Basic EPS is based on the weighted average number of common shares outstanding during each period. Diluted EPS adjusts Basic EPS for the effects of dilutive common stock equivalents outstanding during each period using the treasury stock method. Recently Adopted Accounting Pronouncement Credit Losses On January 1, 2020, we adopted Accounting Standard Update No. 2016-13, Financial Instruments-Credit Losses (Top 326): Measurement of Credit Losses on Financial Instruments with a net increase of our receivables allowance and a related cumulative adjustment to our retained earnings recorded at the beginning of adaption. Upon adoption, we changed our impairment model to utilize a forward-looking current expected credit losses (CECL) model in pace of the incurred loss impairment model for our accounting receivable balance. The cumulative effect adjustment from adoption was immaterial to our condensed consolidated financial statements. Intangibles – Goodwill and Other On January 1, 2020, we adopted Accounting Standard Update No. 2017-04 Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment prospectively. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit's carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The adoption of ASU 2017-04 did not have an impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted Income Taxes In December 2019, the FASB issued Accounting Standard Update No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes. This guidance will be effective for us in the first quarter of 2021 on a prospective basis, and early adoption is permitted. We are currently evaluating the impact of the new guidance on our consolidated financial statements.

Stock Options and Stock-Based E

Stock Options and Stock-Based Employee Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Options and Stock-based Employee Compensation	3. Stock Options and Stock-Based Employee Compensation Below is a summary of common stock options outstanding at December 31, 2020: Authorized Shares Options Outstanding Options Vested Available for Grant Employee and Director Stock Equity Plans: 2004 Stock Option Plan 5,000,000 80,000 80,000 — 2006 Director’s Stock Option Plan 1,100,000 25,000 25,000 — 2012 Incentive Plan 6,300,000 537,010 537,010 — 2018 Omnibus Incentive Plan 6,000,000 100,000 18,750 2,222,521 Israel Plan 400,000 — — 400,000 Total Employee and Director Stock Option Plans: 18,800,000 742,010 660,760 2,622,521 Other Executive Inducement Stock Equity Award 250,000 100,000 — — Total 19,050,000 842,010 660,760 2,622,521 Under all of our stock option plans, new shares are issued when options are exercised. Employee and Director Stock-Based Plans We have non-qualified stock options outstanding to employees and directors under various stock option plans. The plans require the exercise price of options granted under these plans to equal or exceed the fair market value of the Company’s common stock on the date of grant. The options, subject to termination of employment, generally expire ten years from the date of grant. Historically, our employee options and equity awards typically vested pro-rata and annually over three or four years. Stock-based grants to employees, officers and directors frequently contain accelerated vesting provisions upon the occurrence of a change of control, as defined in the applicable option agreements. In connection with the acquisition of CloudAlly (as defined herein), on November 5, 2020, the board authorized a new, non-shareholder-approved equity plan under Nasdaq rules that permit the grant of “inducement” equity award (“Israel Plan”) to employees of CloudAlly who joined Zix as part of the acquisition. Under the terms of the plan, 400,000 awards are available for issuance. These awards are expected to be granted in January 2021 and vest over two to four years. Under the terms of the 2018 Omnibus Incentive Plan approved by our shareholders during our annual meeting held on June 6, 2018, (the “2018 Plan”), 6,000,000 shares are available for issuance. Awards issued under the 2018 Plan typically vest pro-rata and annually over three or four years. Under the terms of the 2012 Incentive Plan adopted by our Board of Directors on April 13, 2012 (the “2012 Plan”), 2,700,000 shares were available for issuance, plus a number of additional shares (not to exceed 1,327,000) underlying options outstanding under certain of the Company’s prior equity plans that thereafter terminate or expire unexercised, or are cancelled, forfeited, or lapse for any reason. Our shareholders approved an Amended and Restated 2012 Incentive Plan during our annual meeting held June 24, 2015, increasing the number of shares available for grant by 3,600,000. Awards issued under the 2012 Plan typically vest pro-rata and annually over three or four years. Other Executive Inducement Stock Equity Award From time to time, we may grant stock equity to key company executives, consultants, and other third parties. In 2020, in connection with a key executive’s joining the company, Zix’s board authorized non-shareholder-approved “inducement” equity awards to him consisting of (a) 100,000 shares of restricted stock, which will vest over four years, (b) 25,000 shares of restricted stock, which will vest in accordance with Zix’s achievement of certain financial performance metrics in 2021 and 2022, and (c) options to acquire 100,000 shares of Zix common stock, which will vest over four years. Accounting Treatment We use the straight-line amortization method for recognizing stock option compensation costs. Our share-based awards include (i) stock options, (ii) restricted stock awards, some of which are subject to time-based vesting (“Restricted Stock”) and some of which are subject to performance-based vesting (“Performance Stock”), and (iii) restricted stock units, some of which are subject to time-based vesting (“RSUs”) and some of which are subject to performance-based vesting (“Performance RSUs”). For the twelve months ended December 31, 2020, 2019, and 2018, respectively, the total stock-based compensation expense resulting from stock options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock was recorded to the following line items of our consolidated statements of comprehensive income (loss): Year Ended December 31, (In thousands) 2020 2019 2018 Cost of revenue $ 1,201 $ 569 $ 327 Research and development expenses 1,641 1,056 469 Selling, general and administrative expenses 6,868 4,626 2,522 Stock-based compensation expense $ 9,710 $ 6,251 $ 3,318 Our stock-based compensation expense has increased yearly due to program expansion associated with our Company growth. A deferred tax asset of $1.9 million, $1.2 million, and $673 thousand resulting from stock-based compensation expense associated with awards relating to the Company’s U.S. operations, was recorded for the twelve months ended December 31, 2020, 2019, and 2018, respectively. As of December 31, 2020, there was $16.7 million of total unrecognized stock-based compensation related to non-vested share-based compensation awards granted under the stock award plans. This cost is expected to be recognized over a weighted average period of 1.9 years. We use the Black-Scholes Option Pricing Model (“BSOPM”) to determine the fair value of option grants. The Company uses the “historical” method to calculate the estimated life of any options that may be granted. The expected stock price volatility is calculated by averaging the historical volatility of the Company’s common stock over a term equal to the expected life of the options. We granted 200,000 options in 2020. We did not grant options in 2019 or 2018. The following weighted average assumptions were applied in determining the fair value of options granted during the respective periods: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.63 % — — Expected option life (years) 5.7 — — Expected stock price volatility 47 % — — Expected dividend yield — — — Fair value of options granted $ 3.15 $ — $ — The assumptions used in the BSOPM valuation are critical as a change in any given factor could have a material impact on the financial results of the Company. The weighted average grant-date fair value of awards of restricted stock and restricted stock units is based on quoted market price of the Company’s common stock on the date of grant. Stock Option Activity The following is a summary of all stock option transactions for the three years ended December 31, 2020: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at January 1, 2018 1,021,314 $ 3.11 Granted at market price — $ 0.00 Cancelled or expired (7,480 ) $ 4.04 Exercised (90,011 ) $ 1.83 Outstanding at December 31, 2018 923,823 $ 3.23 Granted at market price — $ 0.00 Cancelled or expired — $ 0.00 Exercised (167,438 ) $ 2.48 Outstanding at December 31, 2019 756,385 $ 3.39 Granted at market price 200,000 $ 7.37 Cancelled or expired — $ 0.00 Exercised (114,375 ) $ 2.90 Outstanding at December 31, 2020 842,010 $ 4.40 5.14 Options exercisable at December 31, 2020 660,760 $ 3.61 3.93 At December 31, 2020, all 842,010 options outstanding and all 660,760 options exercisable had an exercise price lower than the market value of the Company’s common stock. The aggregate intrinsic value of these options was $3.6 million and $3.3 million, respectively. At December 31, 2019, 756,385 options outstanding and 725,135 options exercisable had an exercise price lower than the market value of the Company’s common stock. The aggregate intrinsic value of these options was $2.6 million and $2.5 million, respectively. The total intrinsic value of options exercised during the years ended December 31, 2020 and 2019, was $514 thousand and $987 thousand, respectively. Summarized information about stock options outstanding at December 31, 2020, is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price $2.00 - $3.49 180,000 1.55 $ 2.67 180,000 $ 2.76 $3.50 - $4.99 462,010 4.65 $ 3.80 462,010 $ 3.80 $5.00 - $6.49 — — — — — $6.50 - $7.99 100,000 9.87 $ 6.70 — — $8.00 - $9.50 100,000 9.18 $ 8.03 18,750 $ 8.03 842,010 5.14 $ 4.40 660,760 $ 3.61 There were 725,135 and 817,573 exercisable options at December 31, 2019 and 2018, respectively. Restricted Stock Activity The following is a summary of all Restricted Stock activity during the three years ended December 31, 2020: Restricted Stock Weighted Average Fair Value Non-vested restricted stock at January 1, 2018 1,082,909 $ 4.57 Granted at market price 842,546 $ 4.53 Vested (419,452 ) $ 4.44 Cancelled (151,003 ) $ 4.77 Non-vested restricted stock at December 31, 2018 1,355,000 $ 4.71 Granted at market price 1,236,579 $ 7.36 Vested (560,497 ) $ 4.66 Cancelled (119,000 ) $ 7.00 Non-vested restricted stock at December 31, 2019 1,912,082 $ 6.26 Granted at market price 1,372,499 $ 7.78 Vested (995,503 ) $ 6.04 Cancelled (197,696 ) $ 6.70 Non-vested restricted stock at December 31, 2020 2,091,382 $ 7.34 Restricted Stock Unit Activity The following is a summary of all RSU activity during the three years ended December 31, 2020: Restricted Stock Units Weighted Average Fair Value Non-vested restricted stock units at January 1, 2018 86,419 $ 4.36 Granted at market price 36,500 $ 4.57 Vested (50,751 ) $ 4.18 Cancelled — $ — Non-vested restricted stock units at December 31, 2018 72,168 $ 4.59 Granted at market price 131,294 $ 8.19 Vested (63,387 ) $ 5.21 Cancelled — $ — Non-vested restricted stock units at December 31, 2019 140,075 $ 7.59 Granted at market price 135,226 $ 8.33 Vested (149,110 ) $ 7.47 Cancelled — $ — Non-vested restricted stock units at December 31, 2020 126,191 $ 8.52 Performance RSU Activity The following is a summary of all Performance RSU activity during the three years ended December 31, 2020: Performance RSUs Weighted Average Fair Value Non-vested performance RSUs at January 1, 2018 39,664 $ 3.98 Granted at market price 5,500 $ 4.04 Vested (32,665 ) $ 3.91 Forfeited — $ 0.00 Non-vested performance RSUs at December 31, 2018 12,499 $ 4.20 Granted at market price 50,000 $ 8.84 Vested (7,000 ) $ 4.08 Forfeited — $ 0.00 Non-vested performance RSUs at December 31, 2019 55,499 $ 8.39 Granted at market price 67,030 $ 7.53 Vested (48,910 ) $ 7.71 Forfeited (4,270 ) $ 8.05 Non-vested performance RSUs at December 31, 2020 69,349 $ 8.07 Performance Stock Activity The following is a summary of all Performance Stock activity during the three years ended December 31, 2020: Performance Stock Weighted Average Fair Value Non-vested performance stock at January 1, 2018 193,110 $ 4.39 Granted at market price 153,723 $ 4.04 Vested (77,874 ) $ 4.26 Forfeited (13,333 ) $ 4.50 Non-vested performance stock at December 31, 2018 255,626 $ 4.22 Granted at market price 417,500 $ 7.15 Vested (123,558 ) $ 4.15 Forfeited (75,000 ) $ 7.15 Non-vested performance stock at December 31, 2019 474,568 $ 6.38 Granted at market price 606,170 $ 7.68 Vested (160,796 ) $ 6.00 Forfeited (68,090 ) $ 6.30 Non-vested performance stock at December 31, 2020 851,852 $ 7.37 The weighted average grant-date fair value of awards of Restricted Stock, RSUs, Performance RSU’s, and Performance Stock is based on the quoted market price of the Company’s common stock on the date of grant.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	4. Supplemental Cash Flow Information Supplemental information relating to interest and taxes: Year Ended December 31, (In thousands) 2020 2019 2018 Interest payments $ 7,619 $ 9,181 $ — Income tax (refunds) payments $ (285 ) $ 493 $ 1,115

Receivables, Net

Receivables, Net	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Receivables, Net	5. Receivables, net (In thousands) December 31, 2020 2019 Gross accounts receivables $ 30,188 $ 21,193 Allowance for credit losses (478 ) — Allowance for returns and doubtful accounts — (265 ) Unpaid portion of deferred revenue (12,879 ) (10,847 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 16,831 $ 10,081 Prior to January 1, 2020, accounts receivable were recorded at cost less an allowance for doubtful accounts. We maintained an allowance for uncollectible accounts receivable for estimated losses resulting from the failure or inability of our customers to make required payments. Subsequent to January 1, 2020, accounts receivable are recorded at cost less an allowance for credit losses. We estimated losses on receivables at the reporting date based on expected losses resulting from the inability of our customers to make required payments, including our historical experience of actual losses and the aging of such receivables. These receivables have been pooled by shared risk characteristics. Based on known information, we may also establish specific reserves for customers in an adverse financial condition or adjust our expectations of changes in conditions that may impact the collectability of outstanding receivables. As of December 31, 2020, based on available information to date, the Company has assessed no material impact related to potential losses caused by COVID-19. The reduction for the unpaid portion of deferred revenue represents future customer service or maintenance obligations which have been billed to customers, but remain unpaid as of the respective balance sheet dates. Deferred revenue on our consolidated balance sheets represents future customer service or maintenance obligations which have been billed and collected as of the respective balance sheet dates. The note receivable represents the remaining outstanding balance of an original note related to the sale of a product line in 2005 in the amount of $540 thousand. This was fully reserved at the time of the sale as the note’s collectability was not assured. The note receivable is fully reserved at December 31, 2020 and 2019.

Prepaid and other current asset

Prepaid and other current assets	12 Months Ended
	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid and other current assets	6. Prepaid and other current assets (In thousands) December 31, 2020 2019 Prepaid insurance, maintenance, software licenses and other $ 4,999 $ 4,881 Tax-related 431 103 Prepaid and other current assets $ 5,430 $ 4,984

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	7. Property and Equipment (In thousands) December 31, 2020 2019 Computer and office equipment and software $ 33,224 $ 30,335 Leasehold improvements 7,844 7,794 Furniture and fixtures 2,954 2,733 Finance lease right-of-use assets 3,362 3,362 47,384 44,224 Less accumulated depreciation (40,039 ) (35,633 ) Property and equipment, net $ 7,345 $ 8,591 Our operations include depreciation expense related to property and equipment of $5.0 million, $5.0 million, and $2.4 million in 2020, 2019, and 2018, respectfully.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	8. Leases Effective January 1, 2019, the Company adopted ASC 842, which requires recognition of a right-of-use asset and lease liability for all leases at the commencement date based on the present value of lease payments over the lease term. Additional qualitative and quantitative disclosures regarding the Company's leasing arrangements are also required. The Company adopted ASC 842 prospectively and elected the package of transition practical expedients that does not require reassessment of (1) whether any existing or expired contracts are or contain leases, (2) lease classification and (3) initial direct costs. In addition, the Company has elected other available practical expedients to not separate lease and non-lease components, which consist principally of common area maintenance charges, for all classes of underlying assets and to exclude leases with an initial term of 12 months or less. The Company determines if a contract is or contains a lease at inception. The Company has operating leases for office spaces and data centers and finance leases for equipment. The Company has entered into lease contracts ranging from 1 to 12 years with the majority of leases having remaining terms one to five years, many of which include options to extend in various increments. Variable lease costs consist primarily of variable common area maintenance, taxes, insurance, parking and utilities. The Company’s leases do not have any residual value guarantees or restrictive covenants. As the implicit rate is not readily determinable for most of the Company’s lease agreements, the Company uses an estimated incremental borrowing rate to determine the initial present value of lease payments. These discount rates for leases are calculated using the Company's weighted average interest rate of the term loan and delayed draw term loan. The components of lease costs are as follows: Year Ended December 31, (In thousands) 2020 2019 Finance lease costs: Amortization of right-of-use asset $ 1,181 $ 1,330 Interest on lease liabilities 85 151 Operating lease costs 4,061 3,490 Short-term lease costs 2,089 2,236 Variable lease costs 829 773 Total lease costs $ 8,245 $ 7,980 Supplemental cash flow information related to leases is as follows: Year Ended December 31, (In thousands) 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows related to operating leases $ 4,130 $ 2,410 Operating cash flows related to finance leases 85 151 Financing cash flows related to finance leases 1,339 1,707 Right-of-use assets obtained in exchange for lease obligations: Operating leases 7,538 7,999 Finance leases — 3,362 Supplemental balance sheet information related to leases is as follows: December 31, (In thousands) Balance Sheet Classification 2020 2019 Operating Leases Operating lease right-of-use asset Operating lease assets $ 14,259 $ 10,128 Total operating lease assets $ 14,259 $ 10,128 December 31, (In thousands) Balance Sheet Classification 2020 2019 Finance Leases Finance lease right-of-use assets $ 3,362 $ 3,362 Accumulated depreciation - finance leases (2,490 ) (1,320 ) Finance lease right-of-use assets, net Property and equipment, net $ 872 $ 2,042 Weighted average remaining lease term and weighted average discount rate are as follows: Weighted Average Remaining Lease Term (Years) Operating leases 3.09 Finance leases 1.34 Weighted Average Discount Rate Operating leases 4.31 % Finance leases 6.13 % Maturities of lease liabilities are as follows: Payments Due by Year Ending December 31, 2021 (In thousands) Total Year 1 Years 2 & 3 Years 4 & 5 Beyond 5 Years Operating leases $ 16,382 $ 5,748 $ 8,356 $ 2,278 $ — Less imputed interest (1,132 ) Total $ 15,250 Finance leases $ 742 $ 626 $ 116 $ — $ — Less imputed interest (26 ) Total $ 716 During the twelve months ended December 31, 2020, we entered into an operating lease for an additional data center, which has not yet commenced and approximately $109 thousand ROU and lease liabilities are expected to be added upon commencement. This operating lease is expected to commence in the first quarter of 2021 with a lease term of 3 years. Additionally, we modified one of our office leases which resulted a write-off of right-of-use assets and lease liability at a value of approximately $438 thousand and $570 thousand, respectively, and a gain of $132 thousand recognized as other income for the twelve month period ended December 31, 2020.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	9. Goodwill and Other Intangible Assets The changes in the carrying amount of goodwill for the years ended December 31, 2020 and 2019, are as follows: Year Ended December 31, (In thousands) 2020 2019 Opening balance $ 171,209 $ 13,783 Additions 22,312 157,121 Acquisition adjustments — — Effect of currency translation adjustment 1,492 305 Goodwill $ 195,013 $ 171,209 Our 2020 acquisition of CloudAlly (as defined herein) resulted in the addition to our goodwill balance in 2020. Our 2019 acquisitions of DeliverySlip (as defined herein) and AppRiver (as defined herein) resulted in the addition to our goodwill balance in 2019. We evaluate goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. There were no impairment indicators to the goodwill recorded as of December 31, 2020. Our other intangible assets consist of the following: December 31, 2020 (In thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Internal use software $ 2,299 $ (923 ) $ 1,376 Internally-developed hosting arrangement 22,886 (5,065 ) 17,821 Trademarks and other 5,503 (1,135 ) 4,368 Technology 59,936 (20,047 ) 39,889 Customer relationships 102,988 (22,668 ) 80,320 Vendor relationship 1,000 (611 ) 389 Intangible assets, net $ 194,612 $ (50,449 ) $ 144,163 December 31, 2019 (In thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Internal use software $ 1,456 $ (504 ) $ 952 Internally-developed hosting arrangement 9,487 (1,258 ) 8,229 Trademarks and other 5,091 (587 ) 4,504 Technology 53,038 (9,851 ) 43,187 Customer relationships 98,879 (10,597 ) 88,282 Vendor relationship 1,000 (278 ) 722 Intangible assets, net $ 168,951 $ (23,075 ) $ 145,876 For the twelve months ended December 31, 2020, amortization of intangible assets was recorded to the following line items of our consolidated statements of operations: Year Ended December 31, (In thousands) 2020 Cost of revenue $ 10,172 Research and development expenses 4,071 Selling, general and administrative expenses 13,070 Amortization of intangible assets $ 27,313 The following table summarizes our estimated future amortization expense: (In thousands) 2021 2022 2023 2024 2025 Thereafter Total Amortization expense $ 30,986 29,998 $ 28,369 $ 20,806 $ 13,611 $ 19,578 $ 143,348

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses	10. Accrued Expenses December 31, (In thousands) 2020 2019 Employee compensation and benefits $ 5,435 $ 7,231 Professional fees 1,038 1,576 Taxes 622 575 Other 3,269 4,350 Total accrued expenses $ 10,364 $ 13,732

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-term Debt	11. Long-term Debt On February 20, 2019, the Company entered into a credit agreement (the “Credit Agreement”) with a syndicate of lenders and SunTrust Bank as administrative agent, which (1) provided for borrowing in the form of a senior secured term loan facility in an aggregate principal amount of $175 million (the “Term Loan”), (2) provided for a senior secured delayed draw term loan facility in an aggregate principal amount of $10 million (the “Delayed Draw Term Loan Facility”), and (3) provided for a senior secured revolving credit facility in an aggregate principal amount of $25 million, up to $5 million of which is available for letters of credit (the “Revolving Facility” and, together with the Term Loan and the Delayed Draw Term Loan Facility, the “Credit Facilities”). On February 20, 2019, the Term Loan was borrowed in full to pay a portion of the purchase price in connection with the AppRiver acquisition (described below in Note 22 “Acquisitions”), including certain fees, costs and expenses related thereto. On May 2, 2019, the Delayed Draw Term Loan Facility was borrowed in full to pay a portion of the purchase price in connection with the DeliverySlip acquisition (described below in Note 22 “Acquisitions”), including certain fees, costs and expenses related thereto. On November 5, 2020, the Company amended its Credit Agreement to, among other things, to borrow an incremental $35.0 million term loan (the “Incremental Term Loan”). The Incremental Term Loan has the same interest rate, maturity date, amortization schedule, collateral and other terms as the existing Term Loan and Delayed Draw Term Loan. The Company used the proceeds of the Incremental Term Loan to fund the acquisition of CloudAlly (described below in Note 22 “Acquisitions”) and to repay all existing borrowing under the Revolving Facility. The Credit Facilities are secured by substantially all the assets of Zix and its wholly-owned domestic subsidiaries and guaranteed by substantially all of Zix’s wholly-owned domestic subsidiaries. Borrowings under the Credit Agreement bear interest, at the Company’s option, at either (1) the adjusted LIBOR rate (as defined in the Credit Agreement) plus a margin ranging from 2.50% to 3.50% or (2) the alternate base rate (as defined in the Credit Agreement) plus a margin ranging from 1.50% to 2.50%. The applicable margin varies depending on the Company’s total net leverage ratio. The Credit Facilities are scheduled to mature on February 20, 2024, unless extended in accordance with the terms of the Credit Agreement. The Credit Agreement includes procedures for additional financial institutions to become lenders, or for any existing lender to increase its commitments thereunder, subject to the limits and conditions set forth in the Credit Agreement. Optional prepayments of borrowings under the Credit Facilities are permitted at any time and do not require any prepayment premium (other than reimbursement of the lenders’ breakage and redeployment costs in the case of a prepayment of LIBOR borrowings). The Credit Agreement contains various financial, operational, and legal covenants. The financial covenant is tested on a quarterly basis, based on the rolling four-quarter period that ends on the last day of each fiscal quarter. The financial covenant requires the Company to maintain a maximum total net leverage ratio of: • 4.75:1.00 for the fiscal quarters ending September 30, 2020 through March 31, 2021; • 4.50:1.00 for the fiscal quarters ending June 30, 2021 through December 31, 2021; and • 4.25:1.00 for the fiscal quarter ending March 31, 2022 and each fiscal quarter thereafter. The non-financial covenants restrict the Company’s ability and the ability of the Company’s restricted subsidiaries to, among other things, incur indebtedness, incur liens, merge with or acquire other entities, make investments, dispose of assets, enter into sale and leaseback transactions, make dividends, distributions or stock repurchases, prepay junior indebtedness, enter into transactions with affiliates, enter into restrictive agreements, and amend organizational documents or the terms of junior indebtedness. The Credit Agreement contains events of default that Zix believes are customary for a secured credit facility. If an event of default relating to bankruptcy or other insolvency events occurs, all obligations under the Credit Agreement will immediately become due and payable. If any other event of default exists under the Credit Agreement, the lenders may accelerate the maturity of the Credit Facilities and exercise other rights and remedies, including foreclosure or other actions against the collateral. If any default exists under the Credit Agreement, or if the Company is unable to make any of the representations and warranties in the Credit Agreement at the applicable time, Zix will be unable to borrow additional funds or have letters of credit issued under the Credit Agreement. Term Loan and Incremental Term Loan As of December 31, 2020, the Company had $206.8 million in principal outstanding under the Term Loan and the Incremental Term Loan. The Term Loan was fully drawn on February 20, 2019 in the amount of $175 million, and requires quarterly payments of principal of $437.5 thousand beginning on June 30, 2019. The Incremental Loan was fully drawn on November 5, 2020 in the amount of $35.0 million, and requires quarterly payments of principal of $89 thousand beginning on December 31, 2020. In addition to other customary mandatory prepayment requirements, the Term Loan and the Incremental Term Loan requires annual prepayments based on a percentage of Zix’s excess cash flow, which percentage will reduce if Zix’s total net leverage ratio decreases. At December 31, 2020, the Company had an outstanding debt balance of $202.0 million attributable to the Term Loan based on the 4.88% interest rate in effect during the period from December 31, 2019 through December 31, 2020. Included in the balance at December 31, 2020 is $4.8 million of unamortized debt issuance costs. Based on the calculation of excess cash flow and total net leverage ratio and for the year ended December 31, 2020, the Company is not required to make prepayment in addition to the quarterly installment. Future scheduled principal payments under the Term Loan as of December 31, 2020 are as follows: (In thousands) Year Ending December 31, Amount 2021 2,105 2022 2,105 2023 2,105 2024 200,534 Total 206,849 Delayed Draw Term Loan Facility At December 31, 2020, the Company had $9.9 million in principal outstanding under the Delayed Draw Term Loan Facility. The Delayed Draw Term Loan Facility was fully drawn on May 2, 2019 in the amount of $10 million to fund the DeliverySlip acquisition. The Delayed Draw Term Loan Facility requires 1.00% per annum amortization of the original principal amount borrowed, payable in equal quarterly installments of $25 thousand beginning on September 30, 2019. In addition to other customary mandatory prepayment requirements, the Delayed Draw Term Loan Facility requires annual prepayments based on a percentage of Zix’s excess cash flow, which percentage reduces if Zix’s total net leverage ratio decreases. At December 31, 2020, the Company had an outstanding debt balance of $9.8 million attributable to the Delayed Draw Term Loan Facility based on the 4.3% interest rate in effect during the period from December 31, 2019 through December 31, 2020. Included in the balance at December 31, 2020 is $34 thousand of unamortized debt issuance costs. Based on the calculation of excess cash flow and total net leverage ratio and for the year ended December 31, 2020, the Company is not required to make prepayment in addition to the quarterly installment. Future scheduled principal payments under the Delayed Draw Term Loan Facility as of December 31, 2020 are as follows: (In thousands) Year Ending December 31, Amount 2021 100 2022 100 2023 100 2024 9,550 Total 9,850 Revolving Facility The Company also has a Revolving Facility with the lenders, pursuant to which the lenders agreed to make a Revolving Facility available to the Company in an aggregate amount of up to $25 million. Proceeds from the Revolving Facility may be used for working capital and general business purposes, including the financing of permitted acquisitions, investments and restricted payments, subject to the conditions contained in the Credit Agreement. Zix is charged a commitment fee ranging from 0.25% to 0.50% per year on the daily amount of the unused portions of the commitments under the Revolving Facility. As of December 31, 2020, the Company had no outstanding debt balance attributable to the Revolving Facility. The undrawn balance of $25 million is available to fund working capital and for other general corporate purposes, including the financing of permitted acquisitions, investments and restricted payments, subject to the conditions contained in the Credit Agreement. For the year ended December 31, 2020, the Company has incurred $78 thousand of commitment fees. As of December 31, 2020, the estimated fair value of the Credit Facilities approximated their carrying value and the Company was in compliance with all covenants in the Credit Agreement.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Preferred Stock	12. Preferred Stock On February 20, 2019, (the “Original Issuance Date” or “Closing Date”), Zix consummated a private placement pursuant to an investment agreement with an investment fund managed by True Wind Capital and issued an aggregate of $100 million of shares of convertible Preferred Stock (as defined below) at a price of $1,000 per share (the “Stated Value”). 64,914 shares of Series A Convertible Preferred Stock (the “Series A Preferred Stock”) were issued for proceeds of $62.7 million, net of issuance costs of $2.3 million, and 35,086 shares of Series B Convertible Preferred Stock (the “Series B Preferred Stock” and, together with the Series A Preferred Stock, the “Preferred Stock”) were issued for proceeds of $33.9 million, net of issuance costs of $1.2 million. The Preferred Stock is classified outside of stockholders’ equity in temporary equity because the shares contain certain redemption features which require redemption upon a change in control. The Series A Preferred Stock can be immediately converted to common stock. On June 5, 2019, Shareholders approved the conversion of the outstanding shares of Series B Preferred Stock into shares of Series A Preferred Stock. Each share of Series B Preferred Stock was converted into the number of shares of Series A Preferred Stock equal to the liquidation preference of such share of Series B Preferred Stock divided by the accreted value of a share of Series A Preferred Stock on the date of conversion plus cash in lieu of fractional shares. On June 6, 2019, all the outstanding shares of Series B Preferred Stock were converted into 35,292 shares of Series A Preferred Stock. As of December 31, 2020, no shares of Series B Preferred Stock are outstanding. The conversion option of the Series A Preferred Stock was determined to have a beneficial conversion feature valued at $2.5 million, excluding the additional beneficial conversion feature accrued for the deemed dividend and was recorded to additional paid-in capital and as a discount to the Series A Preferred Stock. This resulting discount was immediately amortized as the Series A Preferred Stock has no set redemption date but is currently convertible. Dividends The Stated Value of the Series A Preferred Stock accretes at a fixed rate of 8% per annum, compounded quarterly (“Series A Preferred Dividend”). Apart from the Series A Preferred Dividend, the holders of Series A Preferred Stock are also entitled to receive any dividends paid on our common stock on an "as converted" basis. No dividend may be paid on our common stock until such dividend is paid on the Series A Preferred Stock. All calculations of the Accreted Value (as defined below) of Series A Preferred Stock will be computed on the basis of a 360-day year of twelve 30-day months. As of December 31, 2020, the accretion of the Stated Value of Series A Preferred Stock is valued at $15.0 million, including the accretion attributable to the converted Series A Preferred Stock from Series B Preferred Stock, and the accretion of the beneficial conversion feature is valued at $325 thousand. As of June 6, 2019, the accrued dividend on the Series B Preferred Stock, valued at $1.2 million, was converted to Series A Preferred Stock along with the Stated Value of the Series B Preferred Stock. Upon conversion of Series B Preferred Stock to Series A Preferred Stock on June 6, 2019, all remaining dividend calculations are based on the terms of the Series A Preferred Dividend for the converted Series A Preferred Stock. Voting Rights Holders of Series A Preferred Stock are entitled to vote, together with the holders of common stock on all matters submitted to a vote of the holders of our common stock. Each holder of Series A Preferred Stock shall be entitled to the number of votes equal to the largest number of whole shares of common stock into which all shares of Series A Preferred Stock held by such holder could be converted. The vote or consent of the holders of at least a majority of the shares of Series A Preferred Stock outstanding will be necessary for effecting or validating any of the following actions: (i) any amendment, alteration or repeal of Zix’s Articles of Incorporation or Series A Certification of Designations that would adversely affect the rights, preferences, privileges or power of the Series A Preferred Stock; (ii) any amendment or alteration to Zix’s Articles of Incorporation or any other action to authorize or create, or increase the number of authorized or issued shares of capital stock of the Company convertible into shares of, or ranking senior to, or on a parity basis with, the Series A Preferred Stock as to dividend rights or liquidation rights; (iii) the issuance of shares of Series A Preferred Stock after the Original Issuance Date other than in connection with the conversion of Series B Preferred Stock that was issued on the Original Issuance Date; (iv) any action that would cause the Company to cease to be treated as a domestic corporation for U.S. federal income tax purposes; and (v) the incurrence of any indebtedness of the Company that would cause Zix to exceed a specified leverage ratio. Liquidation Preference The Series A Preferred Stock has a liquidation preference equal to the greater of (i) the Stated Value per share as it has accreted as of such date (the “Accreted Value”) and (ii) the amount such holder would have received if the Series A Preferred Stock had converted into common stock immediately prior to such liquidation. Conversion At any time, each Series A Preferred Stock holder may elect to convert each share of such holders’ then-outstanding Series A Preferred Stock into (i) the number of shares of common stock equal to the product of (a) the Accreted Value with respect to such share on the conversion date multiplied by (b) the conversion rate (currently 166.11) as of the applicable conversion date divided by (c) 1,000 plus (ii) cash in lieu of fractional shares. Optional Redemption by Zix At any time after the fourth anniversary of the Closing Date, Zix may redeem the Series A Preferred Stock for an amount per share of Series A Preferred Stock equal to the Accreted Value per share of the Series A Preferred Stock to be redeemed as of the applicable redemption date multiplied by 1.50.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Revenue from Contracts with Customers	13. Revenue from Contracts with Customers Accounting policies Our Company provides message security solutions as subscription services in which we recognize revenue as our services are rendered. Our customer contracts historically have ranged from one to three-year Disaggregation of Revenue In 2020, excluding our CloudAlly sales, we recorded revenue for our services in the following core industry verticals: 21% healthcare, 17% financial services, 3% government sector, and 59% as other. We operate as a single Contract balances Our contract assets include our accounts receivable, discussed in Footnote 5 above, and the deferred cost associated with commissions earned by our sales team on securing new, add-on, and renewal contract orders. During the twelve months ended December 31, 2020 and 2019, we increased our noncurrent deferred contract asset by $4.7 million, and $5.5 million, respectively, resulting from commissions earned by our sales team during the twelve month periods ended December 31, 2020 and 2019. During the twelve months ended December 31, 2020 and 2019, we also amortized $3.7 million and $3.0 million, respectively of deferred cost, as a selling and marketing expense in the related periods. Our deferred cost asset is assessed for impairment on a periodic basis. There were no impairment losses recognized on deferred contract cost assets for each of the twelve months ended December 31, 2020 and 2019. Our contract liabilities consist of deferred revenue representing future customer services which have been billed and collected. The $1.8 million decrease to our net deferred revenue in the twelve months ended December 31, 2020, is primarily related to the timing of orders and payments in the normal course of business and our continued trend toward monthly subscription offset by increase of $1.3 million deferred revenue acquired through CloudAlly (as defined herein) acquisition. The $11.1 million increase to our net deferred revenue in the twelve months ended December 31, 2019, is primarily related to our AppRiver acquisition in February 2019. Performance obligations As of December 31, 2020, the aggregate amount of the transaction prices allocated to remaining service performance obligations, which represents the transaction price of firm orders less inception to date revenue, was $83.4 million. We expect to recognize approximately $62.7 million of revenue related to this backlog in 2021, and $20.7 million in periods thereafter. Approximately $62.4 million of our $218.5 million revenue recognized in the twelve months ended December 31, 2020, was included in our performance obligation balance at the beginning of the period.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	14. Fair Value Measurements FASB guidance regarding fair value measurement establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices for similar assets and liabilities in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions. The following table represents a reconciliation of our acquisition-related contingent earn-out liability measured at fair value on a recurring basis, using Level 3 inputs for the year ended December 31, 2020: (In thousands) Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Balance at December 31, 2019 $ 378 Additions during the period 22 Payments during the period — Adjustments to fair value during the period recorded in General and Administrative expenses — Balance at December 31, 2020 $ 400

Earnings Per Share and Potentia

Earnings Per Share and Potential Dilution	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share and Potential Dilution	15. Earnings Per Share and Potential Dilution Basic earnings per share are computed using the weighted average number of common shares outstanding for the period under the Treasury Stock method. The dilutive effect of potential common shares outstanding is included in diluted earnings per share. The computations for basic and diluted earnings per share for the years ended December 31, 2020, 2019, and 2018, are as follows: Year Ended December 31, 2020 2019 2018 Basic weighted average shares 54,024,162 53,025,152 52,591,714 Effect of dilutive securities: Employee and director stock options — — 347,167 Restricted Stock — — 409,871 RSUs — — 24,369 Performance RSUs — — 9,367 Performance Stock — — 98,807 Potential dilutive common shares 54,024,162 53,025,152 53,481,295 The following table presents the potentially dilutive common shares outstanding that were excluded from the computation of dilutive net loss per share of common stock for the periods presented because including them would have been anti-dilutive: Year Ended December 31, 2020 2019 2018 Stock options to purchase common stock 842,010 756,385 73,313 Restricted Stock 2,091,382 1,912,082 131,774 RSUs 126,191 140,075 6,084 Performance RSUs 69,349 55,499 917 Performance Stock 851,852 474,568 18,536 Preferred Stock 19,135,862 17,668,363 — Potential dilutive common shares 23,116,646 21,006,972 230,624

Significant Customers

Significant Customers	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Significant Customers	16. Significant Customers In 2020, 2019, and 2018, no single customer accounted for 10% or more of our revenues.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. Commitments and Contingencies Our principal commitments consist primarily of obligations under operating and financing leases, which include among others, certain leases of our offices, colocations and servers as well as contractual commitment related network infrastructure and data center operations. Refer to Note 8 “Leases” for our commitments to settle contractual obligations in cash as of December 31, 2020. Claims and Proceedings We are subject to legal proceedings, claims, and litigation against our business. While the outcome of these matters is currently not determinable and the costs and expenses of defending these matters may be significant, we currently do not expect that the ultimate costs to resolve these matters will have a material adverse effect on our consolidated financial statements.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Other Comprehensive Income Loss Tax [Abstract]
Other Comprehensive Income (Loss)	18. Other Comprehensive Income (Loss) The assets and liabilities of international subsidiaries are translated from the respective local currency to the U.S. dollar using exchange rates at the balance sheet date. Related translation adjustments are recorded as a component of the accumulated other comprehensive income (loss). Our Consolidated Statement of Comprehensive Income (Loss) of international subsidiaries are translated from the local currency to the U.S. dollar using average exchange rates for the period. We are exposed to fluctuations in the foreign currency exchange rates as a result of our net investments and international operations. For fiscal year 2020, movements in currency exchange rates and the related impact on the translation of the balance sheets of our subsidiaries in Canada, Israel and the United Kingdom, were the primary cause of our foreign currency translation gain of $1.4 million, net of $440 thousand in income taxes. For fiscal year 2019, movements in currency exchange rates and the related impact on the translation of the balance sheets of our subsidiary in Canada was the primary cause of our foreign currency translation gain of $215 thousand, net of $16 thousand in income taxes. For fiscal year 2018, foreign currency translation adjustments were immaterial.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	19. Income Taxes Components of the income taxes are as follows: (In thousands) 2020 2019 2018 Current: U.S. $ (332 ) $ (341 ) $ (794 ) State 203 216 725 Foreign 79 9 71 Deferred Federal 1,861 (4,365 ) (4,722 ) Foreign (71 ) 3 — Income tax expense (benefit) $ 1,740 $ (4,478 ) $ (4,720 ) The Company’s income tax expense (benefit) for 2020, 2019, and 2018, respectively, reflect tax expense (benefit) based on statutory rates in 2020, 2019, and 2018. A reconciliation of the expected U.S. tax expense (benefit) to income taxes related to continuing operations is as follows: (In thousands) 2020 2019 2018 Expected tax expense at U.S. statutory rate $ (993 ) $ (3,943 ) $ 2,260 Change in corporate tax rate- deferreds — — — Increase (decrease) in valuations allowance 2,681 (295 ) (7,841 ) Increase (decrease) in valuations allowance- other — — — Nondeductible expense and nontaxable income 528 (37 ) 111 State income taxes, net of federal benefits (328 ) (507 ) 815 Foreign income taxes 230 517 68 Other (378 ) (213 ) (133 ) Income tax expense (benefit) $ 1,740 $ (4,478 ) $ (4,720 ) Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Components of our deferred income taxes as of December 31, 2020 and 2019 are as follows: (In thousands) 2020 2019 Deferred tax assets: Nondeductible $ 116 $ 116 U.S. net operating loss carryforwards 48,630 49,657 State net operating loss carryforwards 603 572 Intangible assets 3,169 1,135 Tax credit carryforwards 4,917 5,151 Stock-based compensation 1,943 1,574 Depreciable assets 1,170 1,209 Interest expense 2,111 1,611 Other assets 1,693 1,521 Total deferred tax assets 64,352 62,546 Deferred tax liabilities: Intangible assets (2,125 ) — Revenue recognition (3,222 ) (2,976 ) Prepaid expenses (1,139 ) (997 ) Total deferred tax assets 57,866 58,573 Less valuation allowance (25,233 ) (22,022 ) Net deferred tax assets $ 32,633 $ 36,551 The Company has partially reserved its U.S. net deferred tax assets in 2020, 2019, and 2018 due to the uncertainty of future taxable income. The Company has U.S. federal net operating loss carryforwards of approximately $232 million which begin to expire in 2021. The Company has state credits totaling $1.5 million which can be utilized through 2026 and state net operating losses that have various expiration dates. The Company also has tax credit carryforwards of approximately $3.4 million consisting of business tax credits that begin to expire in 2021. The Company’s net deferred tax assets include a $1.6 million deferred tax liability with Israel associated with the purchase of CloudAlly (see note 22 below). We have determined that utilization of existing net operating losses against future taxable income is not limited by Section 382 of the Internal Revenue Code. Future ownership changes, however, may limit the Company's ability to fully utilize its existing net operating loss carryforwards against any future taxable income. The Company or one of our subsidiaries files income tax returns in the U.S. federal jurisdiction and various states and in the Canadian federal and provincial jurisdictions. We have not taken a tax position that, if challenged, would have a material effect on the financial statements or the effective tax rate for the twelve-months

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Employee Benefit Plan	20. Employee Benefit Plan 401(k) Plan — We have a retirement savings plan structured under Section 401(k) of the Internal Revenue Code covering substantially all of our U.S. employees. Under the plan, contributions are voluntarily made by employees, and we may provide contributions based on the employees’ contributions. Our operating income includes $2.0 million, $1.2 million, and $618 thousand in 2020, 2019, and 2018, respectively, for net contributions from operations to this plan.

Zix Repurchase Program

Zix Repurchase Program	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Zix Repurchase Program	21. Zix Repurchase Program On April 24, 2017, the Company’s Board of Directors approved a share repurchase program that enabled the Company to purchase up to $10 million of its shares of common stock. The shares repurchase program expired on May 31, 2018. The Company did not repurchase shares during the years ended December 31, 2020 or 2019. During the year ended December 31, 2018, the Company repurchased 1,206,994 shares at an aggregate cost of $5.4 million.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Acquisitions	22. Acquisitions Acquisition of CloudAlly On November 5, 2020, Zix acquired 100% of the equity interest of CloudAlly Ltd. (“CloudAlly”) and its parent holding company for a total purchase price of $30.5 million, following a working capital adjustment. The purchase price included cash consideration of $30.0 million, net of cash acquired. The Company used a portion of the proceeds of the Incremental Term Loan (as defined in Note 11) to fund the acquisition of CloudAlly. Founded in 2011, CloudAlly, based in Israel, is a pioneer of enterprise-grade, software-as-a-service (SaaS) cloud backup and recovery solutions. The company offers a robust suite of award-winning, ISO 27001 certified and GDPR/HIPAA compliant solutions for Microsoft Office 365, Google Workspace (formerly G Suite), SharePoint, OneDrive, Salesforce, Box and Dropbox. CloudAlly is a channel-first provider, serving more than 5,000 customers, 500,000 users and supported by 300 Managed Service Provider (MSP) partners. The Company incurred $1.8 million in acquisition-related costs for the year ended December 31, 2020. Revenue from CloudAlly was $1.2 million from the acquisition date November 5, 2020 to December 31, 2020, and due to the continued integration of the combined business, it was impractical to determine earnings attributable to CloudAlly. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is not yet finalized. The majority of the goodwill balance is expected to be deductible for tax purposes. The intangible assets we acquired from CloudAlly consist of technology, customer relationships, and trademarks/names which we are amortizing over 4 years, 4 years and 9 years respectively. The results of operations and the provisional fair values of the acquired assets and liabilities have been included in the accompanying condensed consolidated financial statements since the CloudAlly acquisition closed on November 5, 2020. The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Provisional Fair Value Assets: Current assets $ 1,385 Property and equipment 116 ROU assets 5,080 Trademark/names 390 Technology 6,000 Customer relationships 3,900 Goodwill 22,312 Total assets 39,183 Liabilities: Current liabilities 654 Deferred revenue $ 1,300 Operating lease liabilities 5,080 Deferred tax liability 1,646 Total liabilities 8,680 Net assets recorded $ 30,503 DeliverySlip On May 7, 2019, the Company acquired certain assets of Cirius Messaging Inc. (“Seller”) and its wholly owned subsidiary DeliverySlip Inc.(“DeliverySlip”), related to the DeliverySlip product for a total purchase price of $13.8 million, including cash consideration of $11.4 million and a contingent consideration with an estimated fair value of $2.3 million at the acquisition date. The contingent consideration was paid in full upon the completion of certain agreed upon requirements and a related $0.2 million loss on the contingent consideration was recognized in the year ended December 31, 2019. Included in the cash consideration, a holdback amount of $1.5 million was transferred to an escrow agent for the satisfaction of the Seller’s indemnity and other obligations under the purchase agreement. The acquisition was partially financed with proceeds of $10 million from the Delayed Draw Term Loan Facility. The purchase of DeliverySlip expanded the Company’s product offering including email encryption, e-signatures and secure file solutions. The Company incurred $1.2 million in acquisition-related costs with respect to the DeliverySlip acquisition, which were recorded within operating expenses during the twelve months end December 31, 2019. Prior to the acquisition, approximately 90% of DeliverySlip’s revenue was generated from AppRiver Canada Inc, which became a subsidiary of the Company upon closing of the AppRiver acquisition (as described below). Revenue from additional acquired customers of DeliverySlip for the twelve months ended December 31, 2020 and 2019 were immaterial. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is not yet finalized. The majority of the goodwill balance is expected to be deductible for tax purposes. The intangible asset we acquired from DeliverySlip is technology which we are amortizing over 6 years. The results of operations and the fair values of the acquired assets and liabilities have been included in the accompanying condensed consolidated financial statements since the DeliverySlip acquisition closed on May 7, 2019. Certain estimated values are not yet finalized and subject to revision as additional information becomes available and more detailed analyses are completed. The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Technology $ 4,200 Goodwill 9,603 Total assets 13,803 Liabilities: Deferred revenue $ 52 Total liabilities 52 Net assets recorded $ 13,751 AppRiver Companies On February 20, 2019, Zix acquired 100% of the equity interest of AR Topco, LLC and its subsidiaries, including AppRiver LLC (“AppRiver” and collectively, the “AppRiver Companies”), for a total purchase price of $277.7 million, following a working capital adjustment. The purchase price included cash consideration of $273.1 million, net of cash acquired. This acquisition complements our strategy to accelerate our offerings into the cloud at the point of initial cloud application purchase and expand our customer base. We financed the acquisition with proceeds from (1) cash on hand, (2) the proceeds from the Term Loan, and (3) a private placement with an investment fund managed by True Wind Capital consisting of (i) 64,914 newly issued shares of Series A Convertible Preferred Stock, $1.00 par value per share, and (ii) 35,086 newly issued shares of Series B Convertible Preferred Stock, $1.00 par value per share, in exchange for cash consideration in an aggregate amount of $100 million (which was reduced by $3 million in True Wind Capital’s costs that were reimbursed by the Company). AppRiver is a channel-first provider of cloud-based cyber security and productivity services, offering web protection, email encryption, secure archiving, and email continuity solutions. AppRiver also provides Microsoft Office 365 and Secure Hosted Exchange services, which serve as an effective lead generation tool for AppRiver’s solutions. The acquisition of AppRiver can accelerate our offerings into the cloud at the point of initial cloud application purchase. Because AppRiver currently services over 60,000 worldwide customers using a network of 4,500 Managed Service Providers, this acquisition can also help us expand our customer base. The Company incurred $10.8 million in acquisition-related costs which included $1.1 million, $9.6 million and $98 thousand recorded within operating expenses for the twelve months ended December 31, 2018, December 31, 2019 and December 31, 2020, respectively. Revenue from AppRiver was $137.3 million for the twelve months ended December 31, 2020, and was $97.8 million for the twelve months ended December 31, 2019, since the acquisition date. Due to the continued integration of the combined businesses, it was impracticable to determine earnings attributable to AppRiver. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is not yet finalized. The majority of the goodwill balance is expected to be deductible for tax purposes. The intangible assets we acquired from AppRiver consist of customer relationships, vendor relationships, trademarks/names, and internally developed software, which we are amortizing over 8 years, 3 years, 10 years, and 5-6 years, respectively. The results of operations and the fair values of the acquired assets and liabilities have been included in the accompanying condensed consolidated financial statements since the AppRiver acquisition closed on February 20, 2019. The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 12,200 Property and equipment 3,235 ROU assets 8,778 Customer relationships 91,000 Vendor relationships 1,000 Trademark/Names 4,400 Internally developed software 41,100 Deferred tax asset 3,453 Goodwill 147,518 Total assets 312,684 Liabilities: Current liabilities $ 13,378 Deferred revenue 12,424 Operating lease liabilities 9,178 Total liabilities 34,980 Net assets recorded $ 277,704 Erado On April 2, 2018, the Company acquired all the outstanding capital stock of CM2.COM, Inc., d/b/a Erado (“Erado”) for a total purchase price of $14.4 million, including cash consideration of $11.8 million, net of cash acquired. The purchase of Erado strengthens Zix’s comprehensive archiving solutions with unified archiving, supervision, security, and messaging solutions for customers that demand bundled services. Erado’s long standing focus on helping its customers comply with FINRA and SEC regulations will help further strengthen Zix’s offering for customers with compliance requirements. This acquisition also expands Zix’s cloud-based email archiving capabilities into more than 50 content channels, including social media, instant message, mobile, web, audio, and video. The purchase price includes a holdback of $2.3 million for the satisfaction of certain indemnification claims by the Company, if any, during the two-year The Company incurred $334 thousand in acquisition-related costs which were recorded within operating expenses during the twelve months ended December 30, 2018. We accounted for the acquisition as the purchase of a business and recorded the excess purchase price as goodwill. The goodwill from this transaction is deductible for tax purposes. The intangible assets we acquired from Erado consist of trademarks, internally developed software, and customer relationships, which we are amortizing over an estimated useful life of 5 years, 10 years, and 15 years, respectively. The results of operations and the estimated fair values of the acquired assets and liabilities have been included in the accompanying consolidated financial statements since our April 2, 2018, acquisition date. Revenue from Erado was $3.7 million, and $3.8 million for the twelve months ended December 31, 2020 and 2019, respectively. Revenue was $2.1 million for the twelve months ended December 31, 2018, since the acquisition date. Due to the continued integration of the combined businesses, it was impracticable to determine the earnings. The following table summarizes the estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 848 Property and equipment 169 Trademark/names 260 Technology 3,030 Customer relationships 4,760 Goodwill 6,215 Total assets 15,282 Liabilities: Deferred revenue $ 809 Other current liabilities 93 Total liabilities 902 Net assets recorded $ 14,380 Pro Forma Financial Information (Unaudited) The following unaudited pro forma financial information presents the combined results of operations for the twelve month periods ending December 31, 2020, and 2019, respectively, as though the CloudAlly, DeliverySlip and AppRiver acquisitions that occurred during the reporting period had occurred as of the beginning of the earliest period presented, with adjustments to give effect to pro forma events that are directly attributable to the acquisition, such as amortization expense of intangible assets and acquisition-related transaction costs. These unaudited pro forma results are presented for information purposes only and are not necessarily indicative of what the actual results of operations of the combined company would have been if the acquisition had occurred at the beginning of the earliest period presented, nor are they indicative of future results of operations: Twelve Months Ended December 31, (In thousands, except per share data) 2020 2019 Revenues $ 225,430 $ 200,458 Net (loss) income (6,540 ) 10,617 Basic (loss) per common share $ (0.29 ) $ (0.01 ) Diluted (loss) per common share $ (0.29 ) $ (0.01 ) F-31

Quarterly Results of Operations

Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (Unaudited)	23. Quarterly Results of Operations (Unaudited) The following is a summary of the quarterly results of operations for the years ended December 31, 2020 and 2019: Quarter Ended (In thousands except per share data) March 31 June 30 September 30 December 31 2020 Revenues $ 52,434 $ 53,337 $ 54,840 $ 57,867 Gross margin 26,355 25,079 26,912 27,369 Net (loss) (853 ) (1,902 ) (725 ) (2,945 ) Basic net (loss) attributable to common stockholders* (0.06 ) (0.08 ) (0.05 ) (0.10 ) Diluted net (loss) attributable to common stockholders* (0.06 ) (0.08 ) (0.05 ) (0.10 ) Comprehensive (Loss) (1,758 ) (1,608 ) (232 ) (1,440 ) 2019 Revenues $ 29,300 $ 45,916 $ 47,833 $ 50,380 Gross margin 18,161 25,612 26,411 26,337 Net (loss) (6,265 ) (3,706 ) (1,597 ) (3,079 ) Basic net (loss) attributable to common stockholders* (0.17 ) (0.13 ) (0.07 ) (0.10 ) Diluted net (loss) attributable to common stockholders* (0.17 ) (0.13 ) (0.07 ) (0.10 ) Comprehensive (Loss) (6,297 ) (3,762 ) (1,562 ) (2,812 ) * Net (loss) per share is calculated independently for each quarter. The sum of Net (loss) per share for each quarter may not equal the total Net (loss) per share for the year due to rounding differences.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying consolidated financial statements include the accounts of all our wholly-owned subsidiaries and are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All inter-company accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates — The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reported period. Our significant estimates include primarily those required in the valuation or impairment analysis of goodwill and intangibles, property and equipment, revenue recognition, amortization period of our commission amortization, allowances for doubtful accounts, stock-based compensation, litigation accruals, valuation allowances for deferred tax assets and tax accruals. Although we believe that adequate accruals have been made for unsettled issues, additional gains or losses could occur in future years from resolutions of outstanding matters. These estimates and assumptions take into account historical and forward-looking factors that the Company believes are reasonable, including, but not limited to the potential impacts arising from the recent coronavirus (COVID-19) and public and private sector policies and initiatives aimed at reducing its transmission. As the extent and impacts of the COVID-19 virus remain unclear, the Company’s estimates and assumptions may evolve as conditions change. Actual results could differ materially from original estimates.
Cash Equivalents	Cash Equivalents — Cash investments with maturities of three months or less when purchased are considered cash equivalents
Fair Value of Financial Instruments	Fair Value of Financial Instruments —The Company does not measure the fair value of any financial instrument other than cash equivalents, options, and other equity awards. The carrying values of other financial instruments (receivables and accounts payable) are not recorded at fair value but approximate fair values primarily due to their short-term nature. The carrying values of other current assets and accrued expenses are also not recorded at fair value, but approximate fair values primarily due to their short-term nature. In addition, the Company measures its long-term debt at fair value which approximates book value as the long-term debt bears market rate.
Valuation of Property and Equipment	Valuation of Property and Equipment — The accounting policies and estimates relating to property and equipment are considered significant because of the potential impact that impairment, obsolescence, or change in an asset’s useful life could have on the Company’s operating results. We record an impairment charge on the assets to be held and used when we determine based upon certain triggering events that the carrying value of property and equipment may not be recoverable based on expected undiscounted cash flows attributable to such assets. The amount of a potential impairment is determined by comparing the carrying amount of the asset to either the value determined from a projected discounted cash flow method, using a discount rate that is considered to be commensurate with the risk inherent in the Company’s current business model or the estimated fair market value. Assumptions are made with respect to future net cash flows expected to be generated by the related asset. An impairment charge would be recorded for an amount by which the carrying value of the asset exceeded the discounted projected net cash flows or estimated fair market value. Also, even where a current impairment charge is not necessary, the remaining useful lives are evaluated. No impairment was recorded for any of the periods presented. Property and equipment are recorded at cost and depreciated or amortized using the straight-line method over their estimated useful lives as follows: computer and office equipment and software — three years; leasehold improvements — the shorter of five years or the lease term; and furniture and fixtures — five years. We recorded depreciation expense of $5.0 million for the year ended December 31, 2020. We allocated $4.4 million of the expense to cost of revenue, $377 thousand to research and development expense, and $253 thousand to selling, marketing, and general and administrative expenses.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets — We account for the valuation of goodwill and other intangible assets after classifying intangible assets into three categories: (1) intangible assets with finite lives subject to amortization; (2) intangible assets with indefinite lives not subject to amortization; and (3) goodwill. For intangible assets with finite lives, tests for impairment must be performed if conditions exist that indicate the carrying value may not be recoverable. For intangible assets with indefinite lives and goodwill, tests for impairment must be performed at least annually or more frequently if events or circumstances indicate that assets might be impaired. Goodwill was $195.0 million, or 43%, and $171.2 million, or 41%, of total assets as of December 31, 2020 and 2019, respectively. We evaluate the goodwill for impairment annually in the fourth quarter, or when there is reason to believe that the value has been diminished or impaired. Evaluations for possible impairment are based upon a comparison of the estimated fair value of the reporting unit to which the goodwill has been assigned, versus the sum of the carrying value of the assets and liabilities of that unit including the assigned goodwill value. We include our entire Company as the reporting unit. The fair values used in this evaluation are estimated based on the Company’s market capitalization, which is based on the outstanding stock and market price of the stock. Impairment is deemed to exist if the net book value of the unit exceeds its estimated fair value. No impairment was recorded for any of the periods presented. Our intangible assets with finite lives are amortized using a straight line basis over their economic useful lives.
Deferred Tax Assets	Deferred Tax Assets — Deferred tax assets are recognized if it is “more likely than not” that the benefit of our deferred tax assets will be realized on future federal or state income tax returns. At December 31, 2020, we provided a valuation allowance against a significant portion, $25.2 million, of our accumulated deferred tax assets, reflecting our historical losses and the uncertainty of future taxable income sufficient to utilize net operating loss carryforwards prior to their expiration. Our total deferred tax assets not subject to a valuation allowance are valued at $32.6 million, and consist of $26.9 million of federal net operating loss carryforwards, $4.4 million relating to temporary timing differences between U.S. GAAP and tax-related expense, $1.9 million in federal R&D credits, and $1.0 million relating to U.S. state income tax and other credits. These items are offset by a $1.6 million deferred tax liability associated with our CloudAlly acquisition. If our U.S. taxable income increases from its current level in a future period or if the facts and circumstances on which our estimates and assumptions are based were to change, thereby impacting the likelihood of realizing our deferred tax assets, judgment would have to be applied in determining the amount of valuation allowance no longer required. Reversal of all or a part of this valuation allowance could have a significant positive impact on operating results in the period that it becomes more likely than not that certain of the Company’s deferred tax assets will be realized. Alternatively, should our future income decrease from current levels, a resulting increase to all or a part of this valuation allowance could have a significant negative impact on our operating results
Uncertain Tax Positions	Uncertain Tax Positions — Our Company recognizes and measures uncertain tax positions using a two-step approach. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon settlement.
Right of Use Assets and Lease Obligations	Right-of-use Assets and Lease Obligations — On January 1, 2019, we adopted Accounting Standards Update No. 2016-02, Leases (Topic 842) (ASU 2016-02) using the modified retrospective transition approach by applying the new standard to all leases existing at the date of initial application. Results and disclosure requirements for reporting periods beginning after January 1, 2019, are presented under Topic 842, while prior period amounts have not been adjusted and continue to be reported in accordance with our historical accounting under Topic 840. We elected to combine our lease and non-lease components and to keep leases with an initial term of 12 months or less off the balance sheet and recognize the associated lease payments in the consolidated statements of comprehensive income (loss) on a straight-line basis over the lease term. Additionally, for certain equipment leases, we apply a portfolio approach to effectively account for the finance lease right-of-use (ROU) assets and lease liabilities. Under Topic 842, we determine if an arrangement is a lease at inception. ROU assets and lease liabilities are recognized at commencement date based on the present value of remaining lease payments over the lease term. For this purpose, we consider only payments that are fixed and determinable at the time of commencement. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. Our incremental borrowing rate is the financing rate of our long-term debt at the commencement date. The ROU asset also includes any lease payments made prior to commencement and is recorded net of any lease incentives received. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise such options. When determining the probability of exercising such options, we consider contract-based, asset-based, entity-based, and market-based factors. Our lease agreements may contain variable costs such as common area maintenance, insurance, real estate taxes or other costs. Variable lease costs are expensed as incurred on the consolidated statements of income. Our lease agreements generally do not contain any residual value guarantees or restrictive covenants. Operating leases and finance leases are included in operating lease assets and property and equipment, respectively, on the consolidated balance sheets. Operating lease and finance lease liabilities are separately presented on our consolidated balance sheets.
Revenue Recognition	Revenue Recognition — In May 2014, The Financial Accounting Standards Board (“FASB”) issued ASC 606 which requires revenue recognition when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled to those goods and services. The standard became effective for us in 2018 but did not have a material impact to our revenue recognition process. We earn our revenue from subscription fees for rights related to the use of our software. Approximately 78% of our revenue in 2020 was derived from hosted solutions. While some contracts include one or more performance obligations, the revenue recognition pattern generally is not impacted by separate allocations of these obligations because the services are generally satisfied over the same period of time and revenue is recognized ratably over the contract term. Our subscription terms historically have ranged from one to five years. We are increasingly moving to a monthly subscription model. This shift has been largely driven by our recent acquisition activity. As we further integrate our business, we expect to focus on a monthly subscription model. Revenue is recognized by applying the following steps: • Step 1: Identify the contract(s) with a customer, • Step 2: Identify the performance obligations in the contract, • Step 3: Determine the transaction price • Step 4: Allocate the transaction price to the performance obligations in the contract, and • Step 5: Recognize revenue when (or as) the performance obligation is satisfied. Step 1: Identify the contract(s) with a customer: We consider the terms and conditions of the contract and our customary business practice in identifying our contracts. We determine we have a contract with a customer when the contract is approved, we can identify each party’s rights regarding the services and products transferred, we can identify the payment terms for the services and products, the contract has commercial substance, and it is probable we will be paid. Step 2: Identify the performance obligations in the contract: ASC 606 requires identification and disclosure of performance obligations within a revenue contract. A good or service is considered distinct if the customer can both benefit from the good or service on its own or with other resources that are readily available to the customer, and the promise to transfer the good or service is separately identifiable from other promises in the contract. Step 3: Determine the transaction price: The transaction price is determined based on the consideration we expect to be entitled to receive in exchange for transferring goods and services to the customer. We include variable consideration in the transaction price if we view it as probable that a significant future reduction of cumulative revenue under the contract will not occur. Step 4: Allocate the transaction price to the performance obligations in the contract: We allocate transaction prices to each performance obligation based on the stand-alone selling price of our component services. Step 5: Recognize revenue when (or as) the performance obligation is satisfied: We begin recognize revenue when the customer obtains control of the product or services, at the amount allocated to the satisfied performance obligation. Our performance obligations are generally satisfied over time. While some contracts include one or more performance obligations (including the combined elements noted above along with additional ongoing customer support and other hosted services), the revenue recognition pattern generally is not impacted by the separate allocations of these obligations because the services are generally satisfied over the same period of time and revenue is recognized over the contract period. Discounts provided to customers are recorded as reductions in revenue.
Commission Amortization	Commission Amortization — We amortize our commission costs to expense on a systemic basis over the period of expected benefit to the customer. Determination of the amortization period requires significant judgement. We apply the practical expedient noted in ASC 606-10-10-4 to account for our commission costs and related amortizations at the portfolio level. Additionally, the Company has evaluated commissions earned upon contract renewal as compared to initial commissions paid and determined that because commissions paid were not reasonably proportional to their respective contract values, our renewal commissions could not be considered commensurate with the initial commissions paid. We considered our average contract term length and historical customer retention rates to determine an average length of our customer relationships. We also concluded our add-on sales generally occur halfway into our customer relationships and evaluated our average customer renewal terms. Based on these factors we have determined that 8 years, 4 years and 18 months are the appropriate amortization periods to our new, add-on, and renewal sales commission expenses, respectively. We also perform subsequent assessments for impairment of the related deferred cost asset when indicators present. Following our acquisition of AppRiver in February 2019, we additionally evaluated AppRiver’s sales program to determine whether capitalization of these expenses was appropriate. While we determined certain costs to acquire customers met the capitalization criteria, we also determined renewal commissions earned were commensurate to the initial sales. Based on AppRiver’s primarily month-to-month commitments the Company has chosen to apply the practical expedient approach to immediately recognize such commensurate commission expenses associated with the AppRiver program.
Internal Use Software	Internal Use Software — The Company capitalizes costs related to its cloud email security, productivity and compliance solutions and certain projects for internal use incurred during the application development stage. Costs related to preliminary project activities and post implementation activities are expensed as incurred. Internal-use software is amortized on a straight-line basis over its estimated useful life, which is generally three years. Management evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. In 2020, we capitalized $14.2 million of costs related to internal-use software. The Company expects our capitalization of these costs to increase in the future.
Advertising Expense	Advertising Expense — Advertising costs are expensed as incurred. Our operations include advertising expense of $2.4 million, $4.3 million, and $1.1 million in 2020, 2019, and 2018, respectively
Stock-Based Compensation	Stock-Based Compensation — We currently use the straight-line amortization method for recognizing stock option and restricted stock compensation costs. The measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors are based on the estimated fair value of the awards on the grant dates. The grant date fair value is estimated using either an option-pricing model which is consistent with the terms of the award or a market observed price, if such a price exists. Such cost is recognized over the period during which an employee or director is required to provide service in exchange for the award, i.e., “the requisite service period” (which is usually the vesting period). We also estimate the number of instruments that will ultimately be earned, rather than accounting for forfeitures as they occur.
Earnings Per Share ("EPS")	Earnings Per Share (“EPS”) — Basic EPS is based on the weighted average number of common shares outstanding during each period. Diluted EPS adjusts Basic EPS for the effects of dilutive common stock equivalents outstanding during each period using the treasury stock method.
Recently Adopted Accounting Pronouncement	Recently Adopted Accounting Pronouncement Credit Losses On January 1, 2020, we adopted Accounting Standard Update No. 2016-13, Financial Instruments-Credit Losses (Top 326): Measurement of Credit Losses on Financial Instruments with a net increase of our receivables allowance and a related cumulative adjustment to our retained earnings recorded at the beginning of adaption. Upon adoption, we changed our impairment model to utilize a forward-looking current expected credit losses (CECL) model in pace of the incurred loss impairment model for our accounting receivable balance. The cumulative effect adjustment from adoption was immaterial to our condensed consolidated financial statements. Intangibles – Goodwill and Other On January 1, 2020, we adopted Accounting Standard Update No. 2017-04 Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment prospectively. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit's carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The adoption of ASU 2017-04 did not have an impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted Income Taxes In December 2019, the FASB issued Accounting Standard Update No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes. This guidance will be effective for us in the first quarter of 2021 on a prospective basis, and early adoption is permitted. We are currently evaluating the impact of the new guidance on our consolidated financial statements.
Fair Value Measurements	FASB guidance regarding fair value measurement establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices for similar assets and liabilities in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions.

Stock Options and Stock-Based_2

Stock Options and Stock-Based Employee Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Common Stock Options Outstanding	Below is a summary of common stock options outstanding at December 31, 2020: Authorized Shares Options Outstanding Options Vested Available for Grant Employee and Director Stock Equity Plans: 2004 Stock Option Plan 5,000,000 80,000 80,000 — 2006 Director’s Stock Option Plan 1,100,000 25,000 25,000 — 2012 Incentive Plan 6,300,000 537,010 537,010 — 2018 Omnibus Incentive Plan 6,000,000 100,000 18,750 2,222,521 Israel Plan 400,000 — — 400,000 Total Employee and Director Stock Option Plans: 18,800,000 742,010 660,760 2,622,521 Other Executive Inducement Stock Equity Award 250,000 100,000 — — Total 19,050,000 842,010 660,760 2,622,521
Summary of Total Stock-based Compensation Expense Resulting from Stock Options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock	For the twelve months ended December 31, 2020, 2019, and 2018, respectively, the total stock-based compensation expense resulting from stock options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock was recorded to the following line items of our consolidated statements of comprehensive income (loss): Year Ended December 31, (In thousands) 2020 2019 2018 Cost of revenue $ 1,201 $ 569 $ 327 Research and development expenses 1,641 1,056 469 Selling, general and administrative expenses 6,868 4,626 2,522 Stock-based compensation expense $ 9,710 $ 6,251 $ 3,318
Weighted Average Assumptions Applied in Determining Fair Value of Options Granted	The following weighted average assumptions were applied in determining the fair value of options granted during the respective periods: Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.63 % — — Expected option life (years) 5.7 — — Expected stock price volatility 47 % — — Expected dividend yield — — — Fair value of options granted $ 3.15 $ — $ —
Summary of All Stock Option Transactions	The following is a summary of all stock option transactions for the three years ended December 31, 2020: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Yrs) Outstanding at January 1, 2018 1,021,314 $ 3.11 Granted at market price — $ 0.00 Cancelled or expired (7,480 ) $ 4.04 Exercised (90,011 ) $ 1.83 Outstanding at December 31, 2018 923,823 $ 3.23 Granted at market price — $ 0.00 Cancelled or expired — $ 0.00 Exercised (167,438 ) $ 2.48 Outstanding at December 31, 2019 756,385 $ 3.39 Granted at market price 200,000 $ 7.37 Cancelled or expired — $ 0.00 Exercised (114,375 ) $ 2.90 Outstanding at December 31, 2020 842,010 $ 4.40 5.14 Options exercisable at December 31, 2020 660,760 $ 3.61 3.93
Summarized Information about Stock Options Outstanding by Range of Exercise Prices	Summarized information about stock options outstanding at December 31, 2020, is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number Outstanding Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number Exercisable Weighted Average Exercise Price $2.00 - $3.49 180,000 1.55 $ 2.67 180,000 $ 2.76 $3.50 - $4.99 462,010 4.65 $ 3.80 462,010 $ 3.80 $5.00 - $6.49 — — — — — $6.50 - $7.99 100,000 9.87 $ 6.70 — — $8.00 - $9.50 100,000 9.18 $ 8.03 18,750 $ 8.03 842,010 5.14 $ 4.40 660,760 $ 3.61
Summary of All Restricted Stock Activity	The following is a summary of all Restricted Stock activity during the three years ended December 31, 2020: Restricted Stock Weighted Average Fair Value Non-vested restricted stock at January 1, 2018 1,082,909 $ 4.57 Granted at market price 842,546 $ 4.53 Vested (419,452 ) $ 4.44 Cancelled (151,003 ) $ 4.77 Non-vested restricted stock at December 31, 2018 1,355,000 $ 4.71 Granted at market price 1,236,579 $ 7.36 Vested (560,497 ) $ 4.66 Cancelled (119,000 ) $ 7.00 Non-vested restricted stock at December 31, 2019 1,912,082 $ 6.26 Granted at market price 1,372,499 $ 7.78 Vested (995,503 ) $ 6.04 Cancelled (197,696 ) $ 6.70 Non-vested restricted stock at December 31, 2020 2,091,382 $ 7.34
Summary of All Restricted Stock Unit Activity	The following is a summary of all RSU activity during the three years ended December 31, 2020: Restricted Stock Units Weighted Average Fair Value Non-vested restricted stock units at January 1, 2018 86,419 $ 4.36 Granted at market price 36,500 $ 4.57 Vested (50,751 ) $ 4.18 Cancelled — $ — Non-vested restricted stock units at December 31, 2018 72,168 $ 4.59 Granted at market price 131,294 $ 8.19 Vested (63,387 ) $ 5.21 Cancelled — $ — Non-vested restricted stock units at December 31, 2019 140,075 $ 7.59 Granted at market price 135,226 $ 8.33 Vested (149,110 ) $ 7.47 Cancelled — $ — Non-vested restricted stock units at December 31, 2020 126,191 $ 8.52
Summary of All Performance RSU Activity	The following is a summary of all Performance RSU activity during the three years ended December 31, 2020: Performance RSUs Weighted Average Fair Value Non-vested performance RSUs at January 1, 2018 39,664 $ 3.98 Granted at market price 5,500 $ 4.04 Vested (32,665 ) $ 3.91 Forfeited — $ 0.00 Non-vested performance RSUs at December 31, 2018 12,499 $ 4.20 Granted at market price 50,000 $ 8.84 Vested (7,000 ) $ 4.08 Forfeited — $ 0.00 Non-vested performance RSUs at December 31, 2019 55,499 $ 8.39 Granted at market price 67,030 $ 7.53 Vested (48,910 ) $ 7.71 Forfeited (4,270 ) $ 8.05 Non-vested performance RSUs at December 31, 2020 69,349 $ 8.07
Summary of All Performance Stock Activity	The following is a summary of all Performance Stock activity during the three years ended December 31, 2020: Performance Stock Weighted Average Fair Value Non-vested performance stock at January 1, 2018 193,110 $ 4.39 Granted at market price 153,723 $ 4.04 Vested (77,874 ) $ 4.26 Forfeited (13,333 ) $ 4.50 Non-vested performance stock at December 31, 2018 255,626 $ 4.22 Granted at market price 417,500 $ 7.15 Vested (123,558 ) $ 4.15 Forfeited (75,000 ) $ 7.15 Non-vested performance stock at December 31, 2019 474,568 $ 6.38 Granted at market price 606,170 $ 7.68 Vested (160,796 ) $ 6.00 Forfeited (68,090 ) $ 6.30 Non-vested performance stock at December 31, 2020 851,852 $ 7.37

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Relating to Interest and Taxes	Supplemental information relating to interest and taxes: Year Ended December 31, (In thousands) 2020 2019 2018 Interest payments $ 7,619 $ 9,181 $ — Income tax (refunds) payments $ (285 ) $ 493 $ 1,115

Receivables, Net (Tables)

Receivables, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Summary of Net Receivables	(In thousands) December 31, 2020 2019 Gross accounts receivables $ 30,188 $ 21,193 Allowance for credit losses (478 ) — Allowance for returns and doubtful accounts — (265 ) Unpaid portion of deferred revenue (12,879 ) (10,847 ) Note receivable 458 458 Allowance for note receivable (458 ) (458 ) Receivables, net $ 16,831 $ 10,081

Prepaid and other current ass_2

Prepaid and other current assets (Tables)	12 Months Ended
	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Schedule of Prepaid and Other Current Assets	(In thousands) December 31, 2020 2019 Prepaid insurance, maintenance, software licenses and other $ 4,999 $ 4,881 Tax-related 431 103 Prepaid and other current assets $ 5,430 $ 4,984

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	(In thousands) December 31, 2020 2019 Computer and office equipment and software $ 33,224 $ 30,335 Leasehold improvements 7,844 7,794 Furniture and fixtures 2,954 2,733 Finance lease right-of-use assets 3,362 3,362 47,384 44,224 Less accumulated depreciation (40,039 ) (35,633 ) Property and equipment, net $ 7,345 $ 8,591

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Components of Lease Costs	The components of lease costs are as follows: Year Ended December 31, (In thousands) 2020 2019 Finance lease costs: Amortization of right-of-use asset $ 1,181 $ 1,330 Interest on lease liabilities 85 151 Operating lease costs 4,061 3,490 Short-term lease costs 2,089 2,236 Variable lease costs 829 773 Total lease costs $ 8,245 $ 7,980
Schedule of Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases is as follows: Year Ended December 31, (In thousands) 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows related to operating leases $ 4,130 $ 2,410 Operating cash flows related to finance leases 85 151 Financing cash flows related to finance leases 1,339 1,707 Right-of-use assets obtained in exchange for lease obligations: Operating leases 7,538 7,999 Finance leases — 3,362
Schedule of Supplemental Balance Sheet Information Related to Lease	Supplemental balance sheet information related to leases is as follows: December 31, (In thousands) Balance Sheet Classification 2020 2019 Operating Leases Operating lease right-of-use asset Operating lease assets $ 14,259 $ 10,128 Total operating lease assets $ 14,259 $ 10,128 December 31, (In thousands) Balance Sheet Classification 2020 2019 Finance Leases Finance lease right-of-use assets $ 3,362 $ 3,362 Accumulated depreciation - finance leases (2,490 ) (1,320 ) Finance lease right-of-use assets, net Property and equipment, net $ 872 $ 2,042
Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate	Weighted average remaining lease term and weighted average discount rate are as follows: Weighted Average Remaining Lease Term (Years) Operating leases 3.09 Finance leases 1.34 Weighted Average Discount Rate Operating leases 4.31 % Finance leases 6.13 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities are as follows: Payments Due by Year Ending December 31, 2021 (In thousands) Total Year 1 Years 2 & 3 Years 4 & 5 Beyond 5 Years Operating leases $ 16,382 $ 5,748 $ 8,356 $ 2,278 $ — Less imputed interest (1,132 ) Total $ 15,250 Finance leases $ 742 $ 626 $ 116 $ — $ — Less imputed interest (26 ) Total $ 716

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Changes in Carrying Amount of Goodwill	The changes in the carrying amount of goodwill for the years ended December 31, 2020 and 2019, are as follows: Year Ended December 31, (In thousands) 2020 2019 Opening balance $ 171,209 $ 13,783 Additions 22,312 157,121 Acquisition adjustments — — Effect of currency translation adjustment 1,492 305 Goodwill $ 195,013 $ 171,209
Schedule of Other Intangible Assets	Our other intangible assets consist of the following: December 31, 2020 (In thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Internal use software $ 2,299 $ (923 ) $ 1,376 Internally-developed hosting arrangement 22,886 (5,065 ) 17,821 Trademarks and other 5,503 (1,135 ) 4,368 Technology 59,936 (20,047 ) 39,889 Customer relationships 102,988 (22,668 ) 80,320 Vendor relationship 1,000 (611 ) 389 Intangible assets, net $ 194,612 $ (50,449 ) $ 144,163 December 31, 2019 (In thousands) Gross Carrying Amount Accumulated Amortization Net Carrying Amount Internal use software $ 1,456 $ (504 ) $ 952 Internally-developed hosting arrangement 9,487 (1,258 ) 8,229 Trademarks and other 5,091 (587 ) 4,504 Technology 53,038 (9,851 ) 43,187 Customer relationships 98,879 (10,597 ) 88,282 Vendor relationship 1,000 (278 ) 722 Intangible assets, net $ 168,951 $ (23,075 ) $ 145,876
Schedule of Amortization of Intangible Assets	For the twelve months ended December 31, 2020, amortization of intangible assets was recorded to the following line items of our consolidated statements of operations: Year Ended December 31, (In thousands) 2020 Cost of revenue $ 10,172 Research and development expenses 4,071 Selling, general and administrative expenses 13,070 Amortization of intangible assets $ 27,313
Summary of Estimated Future Amortization Expense	The following table summarizes our estimated future amortization expense: (In thousands) 2021 2022 2023 2024 2025 Thereafter Total Amortization expense $ 30,986 29,998 $ 28,369 $ 20,806 $ 13,611 $ 19,578 $ 143,348

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Summary of Accrued Expenses	December 31, (In thousands) 2020 2019 Employee compensation and benefits $ 5,435 $ 7,231 Professional fees 1,038 1,576 Taxes 622 575 Other 3,269 4,350 Total accrued expenses $ 10,364 $ 13,732

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Term Loan [Member]
Schedule of Future Scheduled Principal Payments	Future scheduled principal payments under the Term Loan as of December 31, 2020 are as follows: (In thousands) Year Ending December 31, Amount 2021 2,105 2022 2,105 2023 2,105 2024 200,534 Total 206,849
Senior Secured Delayed Draw Term Loan Facility [Member]
Schedule of Future Scheduled Principal Payments	Future scheduled principal payments under the Delayed Draw Term Loan Facility as of December 31, 2020 are as follows: (In thousands) Year Ending December 31, Amount 2021 100 2022 100 2023 100 2024 9,550 Total 9,850

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of Reconciliation of Contingent Earn-out Liability Measured at Fair Value on Recurring Basis	The following table represents a reconciliation of our acquisition-related contingent earn-out liability measured at fair value on a recurring basis, using Level 3 inputs for the year ended December 31, 2020: (In thousands) Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Balance at December 31, 2019 $ 378 Additions during the period 22 Payments during the period — Adjustments to fair value during the period recorded in General and Administrative expenses — Balance at December 31, 2020 $ 400

Earnings Per Share and Potent_2

Earnings Per Share and Potential Dilution (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Computations of Basic and Diluted Earnings Per Share	The computations for basic and diluted earnings per share for the years ended December 31, 2020, 2019, and 2018, are as follows: Year Ended December 31, 2020 2019 2018 Basic weighted average shares 54,024,162 53,025,152 52,591,714 Effect of dilutive securities: Employee and director stock options — — 347,167 Restricted Stock — — 409,871 RSUs — — 24,369 Performance RSUs — — 9,367 Performance Stock — — 98,807 Potential dilutive common shares 54,024,162 53,025,152 53,481,295
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following table presents the potentially dilutive common shares outstanding that were excluded from the computation of dilutive net loss per share of common stock for the periods presented because including them would have been anti-dilutive: Year Ended December 31, 2020 2019 2018 Stock options to purchase common stock 842,010 756,385 73,313 Restricted Stock 2,091,382 1,912,082 131,774 RSUs 126,191 140,075 6,084 Performance RSUs 69,349 55,499 917 Performance Stock 851,852 474,568 18,536 Preferred Stock 19,135,862 17,668,363 — Potential dilutive common shares 23,116,646 21,006,972 230,624

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Income Taxes	Components of the income taxes are as follows: (In thousands) 2020 2019 2018 Current: U.S. $ (332 ) $ (341 ) $ (794 ) State 203 216 725 Foreign 79 9 71 Deferred Federal 1,861 (4,365 ) (4,722 ) Foreign (71 ) 3 — Income tax expense (benefit) $ 1,740 $ (4,478 ) $ (4,720 )
Schedule of Reconciliation of Tax Expense Benefit to Income Taxes Related to Continuing Operations	The Company’s income tax expense (benefit) for 2020, 2019, and 2018, respectively, reflect tax expense (benefit) based on statutory rates in 2020, 2019, and 2018. A reconciliation of the expected U.S. tax expense (benefit) to income taxes related to continuing operations is as follows: (In thousands) 2020 2019 2018 Expected tax expense at U.S. statutory rate $ (993 ) $ (3,943 ) $ 2,260 Change in corporate tax rate- deferreds — — — Increase (decrease) in valuations allowance 2,681 (295 ) (7,841 ) Increase (decrease) in valuations allowance- other — — — Nondeductible expense and nontaxable income 528 (37 ) 111 State income taxes, net of federal benefits (328 ) (507 ) 815 Foreign income taxes 230 517 68 Other (378 ) (213 ) (133 ) Income tax expense (benefit) $ 1,740 $ (4,478 ) $ (4,720 )
Components of Deferred Income Taxes	Components of our deferred income taxes as of December 31, 2020 and 2019 are as follows: (In thousands) 2020 2019 Deferred tax assets: Nondeductible $ 116 $ 116 U.S. net operating loss carryforwards 48,630 49,657 State net operating loss carryforwards 603 572 Intangible assets 3,169 1,135 Tax credit carryforwards 4,917 5,151 Stock-based compensation 1,943 1,574 Depreciable assets 1,170 1,209 Interest expense 2,111 1,611 Other assets 1,693 1,521 Total deferred tax assets 64,352 62,546 Deferred tax liabilities: Intangible assets (2,125 ) — Revenue recognition (3,222 ) (2,976 ) Prepaid expenses (1,139 ) (997 ) Total deferred tax assets 57,866 58,573 Less valuation allowance (25,233 ) (22,022 ) Net deferred tax assets $ 32,633 $ 36,551

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2020
Unaudited Pro Forma Financial Information	The following unaudited pro forma financial information presents the combined results of operations for the twelve month periods ending December 31, 2020, and 2019, respectively, as though the CloudAlly, DeliverySlip and AppRiver acquisitions that occurred during the reporting period had occurred as of the beginning of the earliest period presented, with adjustments to give effect to pro forma events that are directly attributable to the acquisition, such as amortization expense of intangible assets and acquisition-related transaction costs. These unaudited pro forma results are presented for information purposes only and are not necessarily indicative of what the actual results of operations of the combined company would have been if the acquisition had occurred at the beginning of the earliest period presented, nor are they indicative of future results of operations: Twelve Months Ended December 31, (In thousands, except per share data) 2020 2019 Revenues $ 225,430 $ 200,458 Net (loss) income (6,540 ) 10,617 Basic (loss) per common share $ (0.29 ) $ (0.01 ) Diluted (loss) per common share $ (0.29 ) $ (0.01 )
CloudAlly Ltd [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Provisional Fair Value Assets: Current assets $ 1,385 Property and equipment 116 ROU assets 5,080 Trademark/names 390 Technology 6,000 Customer relationships 3,900 Goodwill 22,312 Total assets 39,183 Liabilities: Current liabilities 654 Deferred revenue $ 1,300 Operating lease liabilities 5,080 Deferred tax liability 1,646 Total liabilities 8,680 Net assets recorded $ 30,503
Delivery Slip Inc. [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Technology $ 4,200 Goodwill 9,603 Total assets 13,803 Liabilities: Deferred revenue $ 52 Total liabilities 52 Net assets recorded $ 13,751
AppRiver Companies [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the current estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 12,200 Property and equipment 3,235 ROU assets 8,778 Customer relationships 91,000 Vendor relationships 1,000 Trademark/Names 4,400 Internally developed software 41,100 Deferred tax asset 3,453 Goodwill 147,518 Total assets 312,684 Liabilities: Current liabilities $ 13,378 Deferred revenue 12,424 Operating lease liabilities 9,178 Total liabilities 34,980 Net assets recorded $ 277,704
Erado [Member]
Summary of Estimated Fair Value of Acquired Assets and Liabilities	The following table summarizes the estimated fair value of acquired assets and liabilities: (In thousands) Estimated Fair Value Assets: Current assets $ 848 Property and equipment 169 Trademark/names 260 Technology 3,030 Customer relationships 4,760 Goodwill 6,215 Total assets 15,282 Liabilities: Deferred revenue $ 809 Other current liabilities 93 Total liabilities 902 Net assets recorded $ 14,380

Quarterly Results of Operatio_2

Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results of Operations	The following is a summary of the quarterly results of operations for the years ended December 31, 2020 and 2019: Quarter Ended (In thousands except per share data) March 31 June 30 September 30 December 31 2020 Revenues $ 52,434 $ 53,337 $ 54,840 $ 57,867 Gross margin 26,355 25,079 26,912 27,369 Net (loss) (853 ) (1,902 ) (725 ) (2,945 ) Basic net (loss) attributable to common stockholders* (0.06 ) (0.08 ) (0.05 ) (0.10 ) Diluted net (loss) attributable to common stockholders* (0.06 ) (0.08 ) (0.05 ) (0.10 ) Comprehensive (Loss) (1,758 ) (1,608 ) (232 ) (1,440 ) 2019 Revenues $ 29,300 $ 45,916 $ 47,833 $ 50,380 Gross margin 18,161 25,612 26,411 26,337 Net (loss) (6,265 ) (3,706 ) (1,597 ) (3,079 ) Basic net (loss) attributable to common stockholders* (0.17 ) (0.13 ) (0.07 ) (0.10 ) Diluted net (loss) attributable to common stockholders* (0.17 ) (0.13 ) (0.07 ) (0.10 ) Comprehensive (Loss) (6,297 ) (3,762 ) (1,562 ) (2,812 ) * Net (loss) per share is calculated independently for each quarter. The sum of Net (loss) per share for each quarter may not equal the total Net (loss) per share for the year due to rounding differences.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Significant Accounting Policies [Line Items]
Cash investments maturities	3 months
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Depreciation expense	$ 5,000,000	$ 5,000,000	$ 2,400,000
Goodwill	$ 195,013,000	$ 171,209,000	13,783,000
Goodwill to total asset	43.00%	41.00%
Impairment	$ 0	$ 0	0
Accumulated deferred tax assets	25,200,000
Total deferred tax asset not subject to a valuation allowance	32,600,000
Research and development expenses	22,813,000	20,431,000	11,323,000
Advertising expense	$ 2,400,000	$ 4,300,000	$ 1,100,000
Minimum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Software subscription term	1 year
Maximum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Software subscription term	5 years
Customer Concentration Risk [Member] | Sales Revenue Net [Member]
Schedule Of Significant Accounting Policies [Line Items]
Revenue in percentage	78.00%
Federal [Member]
Schedule Of Significant Accounting Policies [Line Items]
Federal net operating loss carryforwards	$ 26,900,000
State [Member]
Schedule Of Significant Accounting Policies [Line Items]
Income tax credits	1,000,000
Foreign [Member]
Schedule Of Significant Accounting Policies [Line Items]
Income tax credits	4,400,000
Federal R&D Credits [Member]
Schedule Of Significant Accounting Policies [Line Items]
Income tax credits	1,900,000
CloudAlly [Member]
Schedule Of Significant Accounting Policies [Line Items]
Deferred tax liabilities	1,600,000
Cost of Revenue [Member]
Schedule Of Significant Accounting Policies [Line Items]
Depreciation expense	4,400,000
Research and Development Expense [Member]
Schedule Of Significant Accounting Policies [Line Items]
Depreciation expense	377,000
Selling, Marketing, and General and Administrative Expenses [Member]
Schedule Of Significant Accounting Policies [Line Items]
Depreciation expense	$ 253,000
New Sales Commission Expenses [Member]
Schedule Of Significant Accounting Policies [Line Items]
Amortization period	8 years
Add-on Sales Commission Expenses [Member]
Schedule Of Significant Accounting Policies [Line Items]
Amortization period	4 years
Renewal Sales Commission Expenses [Member]
Schedule Of Significant Accounting Policies [Line Items]
Amortization period	18 months
Computer [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Office Equipment [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Internally Developed Software [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	3 years
Research and development expenses	$ 14,200,000
Leasehold Improvements [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	5 years
Furniture and Fixtures [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives of depreciated or amortized Property and equipment	5 years

Stock Options and Stock-Based_3

Stock Options and Stock-Based Employee Compensation - Summary of Common Stock Options Outstanding (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 13, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	19,050,000
Options Outstanding	842,010	756,385	923,823	1,021,314
Options Vested	660,760
Available for Grant	2,622,521
2004 Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	5,000,000
Options Outstanding	80,000
Options Vested	80,000
2006 Director's Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	1,100,000
Options Outstanding	25,000
Options Vested	25,000
2018 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	6,000,000				2,700,000
Options Outstanding	100,000
Options Vested	18,750
Available for Grant	2,222,521
2012 Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	6,300,000
Options Outstanding	537,010
Options Vested	537,010
Israel Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	400,000
Available for Grant	400,000
Employee and Director Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	18,800,000
Options Outstanding	742,010
Options Vested	660,760
Available for Grant	2,622,521
Other Executive Inducement Stock Equity Award [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized Shares	250,000
Options Outstanding	100,000

Stock Options and Stock-Based_4

Stock Options and Stock-Based Employee Compensation - Additional Information (Detail) - USD ($)	Nov. 05, 2020	Jun. 24, 2015	Apr. 13, 2012	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiry of option				10 years
Available for Grant				2,622,521
Shares available for issuance				19,050,000
Number of outstanding common stock				842,010	756,385	923,823		1,021,314
Common stock, vesting period				5 years 1 month 20 days
Total unrecognized stock-based compensation related to non-vested stock-based compensation awards				$ 16,700,000
The number of years over which cost is expected to be recognized				1 year 10 months 24 days
Deferred tax assets, tax deferred expense compensation and benefits employee compensation				$ 1,900,000	$ 1,200	$ 673,000
Options granted during period				200,000	0	0
Options outstanding				842,010	756,385	923,823		1,021,314
Options, options exercisable				660,760
Number Exercisable				660,760	725,135	817,573
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of options exercised				$ 514,000	$ 987,000
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding restricted stock				995,503	560,497		419,452
Employee and Director Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding common stock				842,010	756,385
Options outstanding				842,010	756,385
Options, options exercisable				660,760	725,135
Aggregate intrinsic value of options outstanding				$ 3,600,000	$ 2,600,000
Aggregate intrinsic value of options exercisable				$ 3,300,000	$ 2,500,000
2018 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for Grant				2,222,521
Shares available for issuance			2,700,000	6,000,000
Additional shares underlying options outstanding		3,600,000	1,327,000
Number of outstanding common stock				100,000
Options outstanding				100,000
Other Executive Inducement Stock Equity Award [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for issuance				250,000
Number of outstanding common stock				100,000
Options outstanding				100,000
Other Executive Inducement Stock Equity Award [Member] | Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding common stock				100,000
Common stock, vesting period				4 years
Options outstanding				100,000
Other Executive Inducement Stock Equity Award [Member] | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding restricted stock				100,000
Restricted stock, vesting period				4 years
Other Executive Inducement Stock Equity Award [Member] | Achievement Of Financial Performance | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding restricted stock				25,000
CloudAlly Ltd [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for Grant	400,000
Share based payment, award expected granted date	2021-01
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options				3 years
Minimum [Member] | 2018 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options			3 years	3 years
Minimum [Member] | CloudAlly Ltd [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options	2 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options				4 years
Maximum [Member] | 2018 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options			4 years	4 years
Maximum [Member] | CloudAlly Ltd [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options	4 years

Stock Options and Stock-Based_5

Stock Options and Stock-Based Employee Compensation - Summary of Total Stock-based Compensation Expense Resulting from Stock Options, Restricted Stock, RSUs, Performance RSUs, and Performance Stock (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 9,710	$ 6,251	$ 3,318
Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,201	569	327
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,641	1,056	469
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 6,868	$ 4,626	$ 2,522

Stock Options and Stock-Based_6

Stock Options and Stock-Based Employee Compensation - Weighted Average Assumptions Applied in Determining Fair Value of Options Granted (Detail)	12 Months Ended
	Dec. 31, 2020$ / shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	0.63%
Expected option life (years)	5 years 8 months 12 days
Expected stock price volatility	47.00%
Fair value of options granted	$ 3.15

Stock Options and Stock-Based_7

Stock Options and Stock-Based Employee Compensation - Summary of All Stock Option Transactions (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Shares, Outstanding, Beginning Balance	756,385	923,823	1,021,314
Shares, Granted at market price	200,000	0	0
Shares, Cancelled or expired			(7,480)
Shares, Exercised	(114,375)	(167,438)	(90,011)
Shares, Outstanding Ending Balance	842,010	756,385	923,823
Shares, Options Exercisable	660,760
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 3.39	$ 3.23	$ 3.11
Weighted Average Exercise Price, Granted at market price	7.37	0	0
Weighted Average Exercise Price, Cancelled or expired	0	0	4.04
Weighted Average Exercise Price, Exercised	2.90	2.48	1.83
Weighted Average Exercise Price, Outstanding, Ending Balance	4.40	$ 3.39	$ 3.23
Weighted Average Exercise Price, Options Exercisable	$ 3.61
Common stock, vesting period	5 years 1 month 20 days
Weighted Average Remaining Contractual Term, Options exercisable	3 years 11 months 4 days

Stock Options and Stock-Based_8

Stock Options and Stock-Based Employee Compensation - Summarized Information about Stock Options Outstanding by Range of Exercise Prices (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Stock Options [Line Items]
Number of outstanding common stock	842,010	756,385	923,823	1,021,314
Weighted Average Remaining Contractual Life, Options Outstanding	5 years 1 month 20 days
Weighted Average Exercise Price, Options Outstanding	$ 4.40
Number Exercisable	660,760	725,135	817,573
Weighted Average Exercise Price, Options Exercisable	$ 3.61
$2.00 - $3.49 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	2
Range of Exercise Prices, Upper range	$ 3.49
Number of outstanding common stock	180,000
Weighted Average Remaining Contractual Life, Options Outstanding	1 year 6 months 18 days
Weighted Average Exercise Price, Options Outstanding	$ 2.67
Number Exercisable	180,000
Weighted Average Exercise Price, Options Exercisable	$ 2.76
$3.50 - $4.99 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	3.50
Range of Exercise Prices, Upper range	$ 4.99
Number of outstanding common stock	462,010
Weighted Average Remaining Contractual Life, Options Outstanding	4 years 7 months 24 days
Weighted Average Exercise Price, Options Outstanding	$ 3.80
Number Exercisable	462,010
Weighted Average Exercise Price, Options Exercisable	$ 3.80
$5.00 - $6.49 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	5
Range of Exercise Prices, Upper range	6.49
$6.50 - $7.99 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	6.50
Range of Exercise Prices, Upper range	$ 7.99
Number of outstanding common stock	100,000
Weighted Average Remaining Contractual Life, Options Outstanding	9 years 10 months 13 days
Weighted Average Exercise Price, Options Outstanding	$ 6.70
$8.00 - $9.50 [Member]
Schedule Of Stock Options [Line Items]
Range of Exercise Prices, Lower range	8
Range of Exercise Prices, Upper range	$ 9.50
Number of outstanding common stock	100,000
Weighted Average Remaining Contractual Life, Options Outstanding	9 years 2 months 4 days
Weighted Average Exercise Price, Options Outstanding	$ 8.03
Number Exercisable	18,750
Weighted Average Exercise Price, Options Exercisable	$ 8.03

Stock Options and Stock-Based_9

Stock Options and Stock-Based Employee Compensation - Summary of All Restricted Stock Activity (Detail) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance	1,912,082	1,355,000	1,082,909	1,082,909
Shares, Granted at market price	1,372,499	1,236,579		842,546
Shares, Vested	(995,503)	(560,497)		(419,452)
Shares, Cancelled	(197,696)	(119,000)		(151,003)
Shares, Non-vested, Ending balance	2,091,382	1,912,082	1,355,000
Weighted Average Fair Value, Non-vested, Beginning balance	$ 6.26	$ 4.71	$ 4.57	$ 4.57
Weighted Average Fair Value, Granted at market price	7.78	7.36	4.53
Weighted Average Fair Value, Vested	6.04	4.66	4.44
Weighted Average Fair Value, Cancelled	6.70	7	4.77
Weighted Average Fair Value, Non-vested, Ending balance	$ 7.34	$ 6.26	$ 4.71

Stock Options and Stock-Base_10

Stock Options and Stock-Based Employee Compensation - Summary of All Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance	140,075	72,168	86,419
Shares, Granted at market price	135,226	131,294	36,500
Shares, Vested	(149,110)	(63,387)	(50,751)
Shares, Non-vested, Ending balance	126,191	140,075	72,168
Weighted Average Fair Value, Non-vested, Beginning balance	$ 7.59	$ 4.59	$ 4.36
Weighted Average Fair Value, Granted at market price	8.33	8.19	4.57
Weighted Average Fair Value, Vested	7.47	5.21	4.18
Weighted Average Fair Value, Non-vested, Ending balance	$ 8.52	$ 7.59	$ 4.59

Stock Options and Stock-Base_11

Stock Options and Stock-Based Employee Compensation - Summary of All Performance RSU Activity (Detail) - Non-vested Performance RSUs [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance	55,499	12,499	39,664	39,664
Shares, Granted at market price	67,030	50,000	5,500
Shares, Vested	(48,910)	(7,000)	(32,665)
Shares, Cancelled	(4,270)
Shares, Non-vested, Ending balance	69,349	55,499	12,499
Weighted Average Fair Value, Non-vested, Beginning balance	$ 8.39	$ 4.20	$ 3.98	$ 3.98
Weighted Average Fair Value, Granted at market price	7.53	8.84		4.04
Weighted Average Fair Value, Vested	7.71	4.08		3.91
Weighted Average Fair Value, Cancelled	8.05	0		$ 0
Weighted Average Fair Value, Non-vested, Ending balance	$ 8.07	$ 8.39	$ 4.20

Stock Options and Stock-Base_12

Stock Options and Stock-Based Employee Compensation - Summary of All Performance Stock Activity (Details) - Performance Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Non-vested, Beginning balance	474,568	255,626	193,110	193,110
Shares, Granted at market price	606,170	417,500	153,723
Shares, Vested	(160,796)	(123,558)	(77,874)
Shares, Cancelled	(68,090)	(75,000)	(13,333)
Shares, Non-vested, Ending balance	851,852	474,568	255,626
Weighted Average Fair Value, Non-vested, Beginning balance	$ 6.38	$ 4.22	$ 4.39	$ 4.39
Weighted Average Fair Value, Granted at market price	7.68	7.15		4.04
Weighted Average Fair Value, Vested	6	4.15		4.26
Weighted Average Fair Value, Cancelled	6.30	7.15		$ 4.50
Weighted Average Fair Value, Non-vested, Ending balance	$ 7.37	$ 6.38	$ 4.22

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Supplemental Cash Flow Information Relating to Interest and Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Interest payments	$ 7,619	$ 9,181
Income tax (refunds) payments	$ (285)	$ 493	$ 1,115

Receivables, Net - Summary of N

Receivables, Net - Summary of Net Receivables (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts Notes And Loans Receivable Net Current [Abstract]
Gross accounts receivables	$ 30,188	$ 21,193
Allowance for credit losses	478
Allowance for returns and doubtful accounts		(265)
Unpaid portion of deferred revenue	(12,879)	(10,847)
Note receivable	458	458
Allowance for note receivable	(458)	(458)
Receivables, net	$ 16,831	$ 10,081

Receivables, Net - Additional I

Receivables, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Receivables [Abstract]
Note receivable on a product line	$ 540	$ 540
Date of note receivable, reserved	Dec. 31, 2020	Dec. 31, 2019

Prepaid and Other Current Ass_3

Prepaid and Other Current Assets - Schedule of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Prepaid insurance, maintenance, software licenses and other	$ 4,999	$ 4,881
Tax-related	431	103
Prepaid and other current assets	$ 5,430	$ 4,984

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 47,384	$ 44,224
Less accumulated depreciation	(40,039)	(35,633)
Property and equipment, net	7,345	8,591
Computer and Office Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	33,224	30,335
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	7,844	7,794
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	2,954	2,733
Finance Lease Right-of-Use Assets [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 3,362	$ 3,362

Property and Equipment - Additi

Property and Equipment - Additional information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 5	$ 5	$ 2.4

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Lessee Lease Description [Line Items]
Lessee, operating lease, variable lease payment, terms and conditions	Variable lease costs consist primarily of variable common area maintenance, taxes, insurance, parking and utilities.
Lessee, operating lease, existence of option to extend	true
Operating lease liability	$ 109
Lessee, operating lease, lease not yet commenced, term of contract	3 years
Write-off of right-of-use assets	$ 438
Write-off of right-of-use lease liability	570
Other income	$ 132
Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, term of contract	1 year
Lessee, majority operating lease, remaining term of contract	1 year
Maximum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, term of contract	12 years
Lessee, majority operating lease, remaining term of contract	5 years

Leases - Schedule of Components

Leases - Schedule of Components of Lease Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance lease costs:
Amortization of right-of-use asset	$ 1,181	$ 1,330
Interest on lease liabilities	85	151
Operating lease costs	4,061	3,490
Short-term lease costs	2,089	2,236
Variable lease costs	829	773
Total lease costs	$ 8,245	$ 7,980

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Cash Flow Information Related to Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows related to operating leases	$ 4,130	$ 2,410
Operating cash flows related to finance leases	85	151
Financing cash flows related to finance leases	1,339	1,707
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 7,538	7,999
Finance leases		$ 3,362

Leases - Schedule of Suppleme_2

Leases - Schedule of Supplemental Balance Sheet Information Related to Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets And Liabilities Lessee [Abstract]
Operating lease right-of-use asset	$ 14,259	$ 10,128
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Zixi:OperatingLeaseAssetsMember	Zixi:OperatingLeaseAssetsMember
Operating lease assets	$ 14,259	$ 10,128
Finance lease right-of-use assets	3,362	3,362
Accumulated depreciation - finance leases	(2,490)	(1,320)
Finance lease right-of-use assets, net	$ 872	$ 2,042
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentMember	us-gaap:PropertyPlantAndEquipmentMember

Leases - Schedule of Weighted A

Leases - Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate (Detail)	Dec. 31, 2020
Lease Cost [Abstract]
Operating leases, weighted average remaining lease term (years)	3 years 1 month 2 days
Finance leases, weighted average remaining lease term (years)	1 year 4 months 2 days
Operating leases, weighted average discount rate	4.31%
Finance leases, weighted average discount rate	6.13%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Operating Lease Liabilities Payments Due [Abstract]
Operating leases	$ 16,382
Less imputed interest	(1,132)
Total	15,250
Finance leases	742
Less imputed interest	(26)
Total	716
Operating lease payments due, Year 1	5,748
Operating lease payments due, Years 2 & 3	8,356
Operating lease payments due, Years 4 & 5	2,278
Finance lease payments due, Year 1	626
Finance lease payments due, Years 2 & 3	$ 116

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill Roll Forward
Opening balance	$ 171,209	$ 13,783
Additions	22,312	157,121
Effect of currency translation adjustment	1,492	305
Goodwill	$ 195,013	$ 171,209

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 194,612	$ 168,951
Accumulated Amortization	(50,449)	(23,075)
Net Carrying Amount	144,163	145,876
Internal Use Software [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,299	1,456
Accumulated Amortization	(923)	(504)
Net Carrying Amount	1,376	952
Internally-Developed Hosting Arrangement [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	22,886	9,487
Accumulated Amortization	(5,065)	(1,258)
Net Carrying Amount	17,821	8,229
Trademarks and Other [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,503	5,091
Accumulated Amortization	(1,135)	(587)
Net Carrying Amount	4,368	4,504
Technology [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	59,936	53,038
Accumulated Amortization	(20,047)	(9,851)
Net Carrying Amount	39,889	43,187
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	102,988	98,879
Accumulated Amortization	(22,668)	(10,597)
Net Carrying Amount	80,320	88,282
Vendor Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,000	1,000
Accumulated Amortization	(611)	(278)
Net Carrying Amount	$ 389	$ 722

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Schedule of Amortization of Intangible Assets (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 27,313
Cost of Revenue [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	10,172
Research and Development Expense [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	4,071
Selling, General and Administrative Expenses [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 13,070

Goodwill and Other Intangible_7

Goodwill and Other Intangible Assets - Summary of Estimated Future Amortization Expense (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
2021	$ 30,986
2022	29,998
2023	28,369
2024	20,806
2025	13,611
Thereafter	19,578
Total	$ 143,348

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts Payable And Accrued Liabilities Current [Abstract]
Employee compensation and benefits	$ 5,435	$ 7,231
Professional fees	1,038	1,576
Taxes	622	575
Other	3,269	4,350
Total accrued expenses	$ 10,364	$ 13,732

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)	Nov. 05, 2020USD ($)	May 02, 2019USD ($)	Feb. 20, 2019USD ($)	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
Term loan			$ 35,000,000
Outstanding debt balance				$ 202,000,000
Interest rate				4.88%
Unamortized debt issuance costs				$ 4,800,000
Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Delayed draw term loan facility fully drawn date				May 2, 2019
Principal outstanding				$ 9,850,000
Lines of credit, drawn amount		$ 10,000,000
Senior Secured Delayed Draw Term Loan Facility [Member] | 5.67% Interest Rate Effect From May 2, 2019 Through December 31, 2019 [Member]
Debt Instrument [Line Items]
Outstanding debt balance				$ 9,800,000
Interest rate				4.30%
Unamortized debt issuance costs				$ 34,000
Term Loan [Member]
Debt Instrument [Line Items]
Principal outstanding				206,849,000
Lines of credit, drawn amount			$ 175,000,000
Debt instrument quarterly payment, principal amount				437,500
Incremental Term Loan [Member]
Debt Instrument [Line Items]
Lines of credit, drawn amount	$ 35,000,000
Debt instrument quarterly payment, principal amount				89,000
Credit Agreement [Member]
Debt Instrument [Line Items]
Credit facility maturity date			Feb. 20, 2024
Credit Agreement [Member] | Revolving Facility [Member]
Debt Instrument [Line Items]
Outstanding debt balance				0
Undrawn balance				25,000,000
Commitment fees				$ 78,000
Credit Agreement [Member] | Maximum [Member] | Revolving Facility [Member]
Debt Instrument [Line Items]
Percentage of commitment fee unused portions				0.50%
Credit Agreement [Member] | Maximum [Member] | September 30, 2020 through March 30, 2021 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio			4.75
Credit Agreement [Member] | Maximum [Member] | June 30, 2021 through December 31, 2021 [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio			4.50
Credit Agreement [Member] | Maximum [Member] | March 31, 2022 and Each Fiscal Quarter Thereafter [Member]
Debt Instrument [Line Items]
Maximum total net leverage ratio			4.25
Credit Agreement [Member] | Maximum [Member] | LIBO Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate			3.50%
Credit Agreement [Member] | Maximum [Member] | Alternate Base Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate			2.50%
Credit Agreement [Member] | Minimum [Member] | Revolving Facility [Member]
Debt Instrument [Line Items]
Percentage of commitment fee unused portions				0.25%
Credit Agreement [Member] | Minimum [Member] | LIBO Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate			2.50%
Credit Agreement [Member] | Minimum [Member] | Alternate Base Rate [Member]
Debt Instrument [Line Items]
Debt instrument bear interest rate			1.50%
Credit Agreement [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt instrument quarterly payment, principal amount				$ 25,000
Amortization payments percentage of original aggregate principal amount				1.00%
Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Aggregate principal amount				$ 25,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount			$ 175,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount			10,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Aggregate principal amount			25,000,000
AppRiver Companies [Member] | Credit Agreement [Member] | Syndicate of Lenders and SunTrust Bank [Member] | Senior Secured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Letters of credit			$ 5,000,000
Delivery Slip Acquisition [Member] | Credit Agreement [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Delayed draw term loan facility fully drawn date			May 2, 2019

Long-term Debt - Schedule of Fu

Long-term Debt - Schedule of Future Scheduled Principal Payments Under Term Loan (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Term Loan [Member]
Debt Instrument [Line Items]
2021	$ 2,105
2022	2,105
2023	2,105
2024	200,534
Total	206,849
Senior Secured Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
2021	100
2022	100
2023	100
2024	9,550
Total	$ 9,850

Preferred Stock - Additional In

Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 06, 2019	Feb. 20, 2019	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Preferred stock, shares outstanding			0	0
Beneficial conversion feature, valued			$ 2,500
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible Preferred stock, par value			$ 1	$ 1
Convertible Preferred stock, shares issued		64,914	100,206	100,206
Issuance of preferred stock in connection with private placement		$ 62,700
Preferred stock, net of issuance costs		$ 2,300	$ 2,253
Preferred stock, number of shares converted	35,292
Accretion of beneficial conversion feature valued			125	$ 99
Accrued dividend on preferred stock			5,754	6,159
Series B Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Convertible Preferred stock, shares issued		35,086
Issuance of preferred stock in connection with private placement		$ 33,900
Preferred stock, net of issuance costs		1,200	$ 1,204
Preferred stock, shares outstanding			0
Accretion of beneficial conversion feature valued			$ 67	35
Accrued dividend on preferred stock			$ 3,079	$ 1,030
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock accretion percentage			8.00%
Accretion of stated value of preferred stock			$ 15,000
Preferred stock conversion description			At any time, each Series A Preferred Stock holder may elect to convert each share of such holders’ then-outstanding Series A Preferred Stock into (i) the number of shares of common stock equal to the product of (a) the Accreted Value with respect to such share on the conversion date multiplied by (b) the conversion rate (currently 166.11) as of the applicable conversion date divided by (c) 1,000 plus (ii) cash in lieu of fractional shares.
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Accretion of beneficial conversion feature valued			$ 325
Accrued dividend on preferred stock	$ 1,200
True Wind Capital [Member]
Temporary Equity [Line Items]
Aggregate purchase price of preferred stock issued in private placement		$ 100,000
Convertible Preferred stock, par value		$ 1,000

Revenue from Contracts with C_2

Revenue from Contracts with Customers - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 30, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)Segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Disaggregation Of Revenue [Line Items]
Number of operating segment | Segment									1
Percentage of revenue generated from email protection services									100.00%	100.00%
Increased noncurrent deferred contract asset									$ 4,700,000	$ 5,500,000
Amortization of deferred cost									3,700,000	3,000,000
Impairment losses recognized on deferred contract cost assets									0	0
Increase (decrease) to net deferred revenue									(1,800,000)
Revenue recognized performance obligation									62,400,000
Revenue recognized	$ 57,867,000	$ 54,840,000	$ 53,337,000	$ 52,434,000	$ 50,380,000	$ 47,833,000	$ 45,916,000	$ 29,300,000	218,478,000	173,428,000	$ 70,478,000
AppRiver Companies [Member]
Disaggregation Of Revenue [Line Items]
Increase (decrease) to net deferred revenue										$ 11,100,000
CloudAlly [Member]
Disaggregation Of Revenue [Line Items]
Increase (decrease) to net deferred revenue									$ 1,300,000
Healthcare [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage									21.00%
Financial Services [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage									17.00%
Government Sector [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage									3.00%
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue in precentage									59.00%
Minimum [Member]
Disaggregation Of Revenue [Line Items]
Subscription services contracts period									1 year
Maximum [Member]
Disaggregation Of Revenue [Line Items]
Subscription services contracts period									3 years

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Additional Information (Detail 1) $ in Millions	Dec. 31, 2020USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period	1 year
Revenue remaining service performance obligations	$ 83.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period	1 year
Revenue remaining service performance obligations	$ 62.7
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Disaggregation Of Revenue [Line Items]
Revenue, remaining performance obligation expected timing of satisfaction period	1 year
Revenue remaining service performance obligations	$ 20.7

Fair Value Measures - Schedule

Fair Value Measures - Schedule of Reconciliation of Contingent Earn-out Liability Measured at Fair Value on Recurring Basis (Detail) - Level 3 [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2019	$ 378
Additions during the period	22
Balance at December 31, 2020	$ 400

Earnings Per Share and Potent_3

Earnings Per Share and Potential Dilution - Computations of Basic and Diluted Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Number of Shares [Line Items]
Basic weighted average shares	54,024,162	53,025,152	52,591,714
Potential dilutive common shares	54,024,162	53,025,152	53,481,295
Employee and Director Stock Options [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities			347,167
Restricted Stock [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities			409,871
RSUs [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities			24,369
Performance RSUs [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities			9,367
Performance Stock [Member]
Weighted Average Number of Shares [Line Items]
Effect of dilutive securities			98,807

Earnings Per Share and Potent_4

Earnings Per Share and Potential Dilution - Computations of Basic and Diluted Earnings Per Share Excluded From Potentially Dilutive Common Shares Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	23,116,646	21,006,972	230,624
Stock Options to Purchase Common Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	842,010	756,385	73,313
Restricted Stock
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	2,091,382	1,912,082	131,774
Restricted Stock Units (RSUs) [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	126,191	140,075	6,084
Non-vested Performance RSUs [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	69,349	55,499	917
Performance Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	851,852	474,568	18,536
Preferred Stock [Member]
Weighted Average Number of Shares [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	19,135,862	17,668,363

Significant Customers - Additio

Significant Customers - Additional Information (Detail) - Customer	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transactions [Abstract]
Customer accounted for revenue	0	0	0

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Foreign currency translation loss, net of tax	$ (1,387)	$ (215)	$ 16
Canada [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Foreign currency translation loss, net of tax	1,400	215
Foreign currency translation loss, tax amount	$ 440	$ 16

Income Taxes - Components of In

Income Taxes - Components of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
U.S.	$ (332)	$ (341)	$ (794)
State	203	216	725
Foreign	79	9	71
Deferred
Federal	1,861	(4,365)	(4,722)
Foreign	(71)	3
Income tax expense (benefit)	$ 1,740	$ (4,478)	$ (4,720)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Tax Expense Benefit to Income Taxes Related to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Expected tax expense at U.S. statutory rate	$ (993)	$ (3,943)	$ 2,260
Increase (decrease) in valuations allowance	2,681	(295)	(7,841)
Nondeductible expense and nontaxable income	528	(37)	111
State income taxes, net of federal benefits	(328)	(507)	815
Foreign income taxes	230	517	68
Other	(378)	(213)	(133)
Income tax expense (benefit)	$ 1,740	$ (4,478)	$ (4,720)

Income Taxes - Components of De

Income Taxes - Components of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities:
Less valuation allowance	$ (25,200)
Net deferred tax assets	32,600
US [Member]
Deferred tax assets:
Nondeductible	116	$ 116
U.S. net operating loss carryforwards	48,630	49,657
State net operating loss carryforwards	603	572
Intangible assets	3,169	1,135
Tax credit carryforwards	4,917	5,151
Stock-based compensation	1,943	1,574
Depreciable assets	1,170	1,209
Interest expense	2,111	1,611
Other assets	1,693	1,521
Total deferred tax assets	64,352	62,546
Deferred tax liabilities:
Intangible assets	(2,125)
Revenue recognition	(3,222)	(2,976)
Prepaid expenses	(1,139)	(997)
Total deferred tax assets	57,866	58,573
Less valuation allowance	(25,233)	(22,022)
Net deferred tax assets	$ 32,633	$ 36,551

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Income Taxes [Line Items]
Deferred tax assets	$ 32.6
Unrecognized tax benefits to significantly increase or decrease	12 months
Statute of limitations by major tax jurisdictions	3 years
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 232
U.S. net operating loss carryforwards expire	2021
State [Member]
Income Taxes [Line Items]
State tax credit carryforwards	$ 1.5
Operating loss carryforwards, expiration dates	2026
General Business Tax Credit Carry Forward [Member]
Income Taxes [Line Items]
State tax credit carryforwards	$ 3.4
Tax credit carry forward began to expiration	2021
General Business Tax Credit Carry Forward [Member] | CloudAlly [Member]
Income Taxes [Line Items]
Deferred tax assets	$ 1.6

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Net contribution from operations to employee benefit plan	$ 2,000	$ 1,200	$ 618

Zix Repurchase Program - Additi

Zix Repurchase Program - Additional Information (Detail) - USD ($)	Apr. 24, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount	$ 10,000,000
Share repurchase program expiration date	May 31, 2018
Treasury repurchase program				$ 5,393,000
January 2016 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		0	0		1,206,994
Treasury repurchase program					$ 5,400,000

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Thousands	Nov. 05, 2020USD ($)CustomerUserServiceProvider	May 07, 2019USD ($)	May 06, 2019	Feb. 20, 2019USD ($)CustomerServiceProvider$ / sharesshares	Apr. 02, 2018USD ($)Channel	Dec. 31, 2020USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)	Dec. 30, 2018USD ($)
Business Acquisition [Line Items]
Cash consideration						$ 30,046	$ 284,590	$ 11,773
Series A Convertible Preferred Stock [Member]
Business Acquisition [Line Items]
Preferred stock, par value | $ / shares						$ 1	$ 1
True Wind Capital [Member]
Business Acquisition [Line Items]
Preferred stock, par value | $ / shares				$ 1,000
Investment agreement aggregate cash consideration				$ 100,000
Delivery Slip Inc. [Member] | AppRiver Companies [Member]
Business Acquisition [Line Items]
Revenue generated from AppRiver Canada Inc			90.00%
CloudAlly Ltd [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired	100.00%
Total purchase price	$ 30,500
Cash consideration	$ 30,000
Number of customers | Customer	5,000
Number of users | User	500,000
Number of managed service providers | ServiceProvider	300
Acquisition related costs						$ 1,800
Revenue from acquisition						$ 1,200
Acquisition date started						Nov. 5, 2020
Effective date of acquisition						Dec. 31, 2020
CloudAlly Ltd [Member] | Technology [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	4 years
CloudAlly Ltd [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	4 years
CloudAlly Ltd [Member] | Trademark/names [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live	9 years
Delivery Slip Inc. [Member]
Business Acquisition [Line Items]
Total purchase price		$ 11,400
Acquisition related costs							$ 1,200
Intangible assets, estimated useful live						6 years
Total purchase price		13,800
Contingent consideration liability		2,300
Loss on business combination contingent consideration							(200)
Cash consideration paid through escrow deposit		1,500
Delivery Slip Inc. [Member] | Senior Secured Delayed Draw Term Loan Facility [Member]
Business Acquisition [Line Items]
Aggregate principal amount		$ 10,000
AppRiver Companies [Member]
Business Acquisition [Line Items]
Percentage of equity interest acquired				100.00%
Cash consideration				$ 273,100
Number of customers | Customer				60,000
Number of managed service providers | ServiceProvider				4,500
Acquisition related costs						$ 10,800
Total purchase price				$ 277,700
Business combination, revenue						137,300	97,800
AppRiver Companies [Member] | Operating Expenses [Member]
Business Acquisition [Line Items]
Acquisition related costs						98	9,600	1,100
AppRiver Companies [Member] | True Wind Capital [Member] | Series A Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Preferred stock, shares, new issue | shares				64,914
Preferred stock, par value | $ / shares				$ 1
AppRiver Companies [Member] | True Wind Capital [Member] | Series B Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Preferred stock, shares, new issue | shares				35,086
Preferred stock, par value | $ / shares				$ 1
AppRiver Companies [Member] | True Wind Capital [Member] | Series A and B Convertible Preferred Stock [Member] | Private Placement [Member]
Business Acquisition [Line Items]
Investment agreement aggregate cash consideration				$ 100,000
Reduction in costs, that were reimbursed				$ 3,000
AppRiver Companies [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live				8 years
AppRiver Companies [Member] | Trademark/names [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live				10 years
AppRiver Companies [Member] | Vendor Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live				3 years
AppRiver Companies [Member] | Internally Developed Software [Member] | Minimum [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live				5 years
AppRiver Companies [Member] | Internally Developed Software [Member] | Maximum [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live				6 years
Erado [Member]
Business Acquisition [Line Items]
Cash consideration					$ 11,800
Acquisition related costs									$ 334
Total purchase price					14,400
Cash consideration paid through escrow deposit					$ 2,300
Business combination, revenue						$ 3,700	$ 3,800	$ 2,100
Number of channels | Channel					50
Escrow account certain indemnification claims, period					2 years
Holdback amount released to selling shareholders upon one year anniversary of closing acquisition					$ 1,100
Holdback released to selling shareholders, description						An amount equal to $1.1 million of the holdback amount, less any amounts paid or otherwise subject to an outstanding claim for indemnification, was released to the selling shareholders upon the one year anniversary of the closing of the acquisition
Erado [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live					15 years
Erado [Member] | Internally Developed Software [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live					10 years
Erado [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Intangible assets, estimated useful live					5 years

Acquisitions - Summary of Estim

Acquisitions - Summary of Estimated Fair Value of Acquired Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Nov. 05, 2020	Dec. 31, 2019	May 07, 2019	Feb. 20, 2019	Dec. 31, 2018	Apr. 02, 2018
Assets:
Goodwill	$ 195,013		$ 171,209			$ 13,783
CloudAlly Ltd [Member]
Assets:
Current assets		$ 1,385
Property and equipment		116
ROU assets		5,080
Goodwill		22,312
Total assets		39,183
Liabilities:
Current liabilities		654
Deferred revenue		1,300
Operating lease liabilities		5,080
Deferred tax liabilities		1,646
Total liabilities		8,680
Net assets recorded		30,503
Delivery Slip Inc. [Member]
Assets:
Goodwill				$ 9,603
Total assets				13,803
Liabilities:
Deferred revenue				52
Total liabilities				52
Net assets recorded				13,751
AppRiver Companies [Member]
Assets:
Current assets					$ 12,200
Property and equipment					3,235
ROU assets					8,778
Goodwill					147,518
Total assets					312,684
Deferred tax asset					3,453
Liabilities:
Current liabilities					13,378
Deferred revenue					12,424
Operating lease liabilities					9,178
Total liabilities					34,980
Net assets recorded					277,704
Erado [Member]
Assets:
Current assets							$ 848
Property and equipment							169
Goodwill							6,215
Total assets							15,282
Liabilities:
Deferred revenue							809
Total liabilities							902
Other current liabilities							93
Net assets recorded							14,380
Technology [Member] | CloudAlly Ltd [Member]
Assets:
Intangible assets		6,000
Technology [Member] | Delivery Slip Inc. [Member]
Assets:
Intangible assets				$ 4,200
Technology [Member] | Erado [Member]
Assets:
Intangible assets							3,030
Trademark/names [Member] | CloudAlly Ltd [Member]
Assets:
Intangible assets		390
Trademark/names [Member] | AppRiver Companies [Member]
Assets:
Intangible assets					4,400
Trademark/names [Member] | Erado [Member]
Assets:
Intangible assets							260
Customer Relationships [Member] | CloudAlly Ltd [Member]
Assets:
Intangible assets		$ 3,900
Customer Relationships [Member] | AppRiver Companies [Member]
Assets:
Intangible assets					91,000
Customer Relationships [Member] | Erado [Member]
Assets:
Intangible assets							$ 4,760
Vendor Relationships [Member] | AppRiver Companies [Member]
Assets:
Intangible assets					1,000
Internally Developed Software [Member] | AppRiver Companies [Member]
Assets:
Intangible assets					$ 41,100

Acquisitions - Unaudited Pro Fo

Acquisitions - Unaudited Pro Forma Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition Pro Forma Information [Abstract]
Revenues	$ 225,430	$ 200,458
Net (loss) income	$ (6,540)	$ 10,617
Basic (loss) per common share	$ (0.29)	$ (0.01)
Diluted (loss) per common share	$ (0.29)	$ (0.01)

Quarterly Results of Operatio_3

Quarterly Results of Operations (Unaudited) - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 57,867	$ 54,840	$ 53,337	$ 52,434	$ 50,380	$ 47,833	$ 45,916	$ 29,300	$ 218,478	$ 173,428	$ 70,478
Gross margin	27,369	26,912	25,079	26,355	26,337	26,411	25,612	18,161	105,715	96,520	55,292
Net income (loss)	$ (2,945)	$ (725)	$ (1,902)	$ (853)	$ (3,079)	$ (1,597)	$ (3,706)	$ (6,265)	$ (6,425)	$ (14,647)	$ 15,444
Basic net (loss) attributable to common stockholders*	$ (0.10)	$ (0.05)	$ (0.08)	$ (0.06)	$ (0.10)	$ (0.07)	$ (0.13)	$ (0.17)	$ (0.29)	$ (0.46)	$ 0.29
Diluted net (loss) attributable to common stockholders*	$ (0.10)	$ (0.05)	$ (0.08)	$ (0.06)	$ (0.10)	$ (0.07)	$ (0.13)	$ (0.17)	$ (0.29)	$ (0.46)	$ 0.29
Comprehensive (Loss)	$ (1,440)	$ (232)	$ (1,608)	$ (1,758)	$ (2,812)	$ (1,562)	$ (3,762)	$ (6,297)	$ (5,038)	$ (14,432)	$ 15,428